RESOLVED! Flex Builder 3 Debugger Stopped Working!!

Posted: March 11, 2008 in Adobe, Flex


This one shall never be forgotten. After a couple hours more of troubleshooting this issue I returned to a dialog setting I visited once before. But this time I tried something a little different;

As I stated before, if I debug my Flex app, the app runs in the browser but the debugger is unable to connect. So I ran it again. As the debugger was trying to connect I went to the running app in the browser. I right-clicked on the app bringing up the Flash Player context menu. I clicked on the Debugger menu item (see image below).

Debugger in Menu

This then brought up the familiar Flash Player Debugger dialog box (see image below)

Debugger Setting

Now in the past I would simply click on the Connect button, but with no success. I then decided to specify Other Machine and entering my localhost IP address (I tried entering Localhost without success). I then clicked on the Connect button. Suddenly a change occurred on the Flex Builder interface. I first though that the process of waiting for the debugger to connect timed out, but Low and Behold! The debugger connected!! I couldn’t believe my eyes. Was it that simple all along? I stopped the debugger and started it again with my breakpoints. Again the debugger connected … without complaint. I am now a happy camper.

I’ve been suffering headaches for the past couple of days (even today). This issue only served to make them worse. I even dreamed about it last night. However now I can clear my mind and rest easy that my Flex Builder Debugger is Back! (unfortunately so are my headaches)

Thanks all who commented on my last post for the help. Even though none of them provided a solution, I learned a lot along the way.

  1. If you need to do that, maybe you don’t have the latest debug Player.

  2. therush says:

    Hi Tom,

    Actually, I used the code in my previous post to confirm that I am using the very latest version of the Debug Flash Player. In addition, I have uninstalled the Flash Player (using the Adobe supplied uninstaller), reinstalled the Debug Flash Player, and restarted the PC several times.

    By the way, the debugger never stopped working when debugging AIR apps. In fact I ported my Flex 3 app to n AIR app and continued my testing and debugging the Flex app as an AIR app. That was a learning exercise in itself. I have to encapsulate the Flex specific script and the AIR specific script into two different classes. Then depending on which project I am working with (Flex or AIR) it would use the appropriate classes. Fortunatly I deployed the Flex app as an AIR app and not the other way around.

    Thanks for the tip anyway.

  3. Tom Carden says:

    Brilliant! Thanks for posting this, I’ve been googling on and off for a few weeks now trying to find out how to re-enable break-points since I updated some combination of flash player, flex builder and mac os. Setting the local IP address specifically fixed it for me too.

    Definitely a weird bug, since the debugger was working perfectly when an error was thrown, but the debug player would hang if any breakpoints were set.

    Thanks again!

  4. Johanes says:

    Awesome! thanks dude for publishing this, finally I found out what went wrong and my Flex Builder can connect back to debugger.

    Thanks heaps!

  5. Mitek says:

    I had the same problem and after reading this post I right-clicked on Debugger and there I saw really weird thing – it was trying to connect to 192.168.100 (non-existing address in my network), so I simply selected the Localhost and it worked.

    Thanks for the post!


  6. Saqlain Abbas says:

    Excellent!! thanks therush. It also solved my problem 🙂

  7. vijay says:

    Thanks a lot man….. it really helped me ……. i was unable 2 connect to debugger since two days now it got resolved …. now i hope i can meet my deadline if everything else goes right 🙂

  8. riasol says:

    Thanks for your publication. I had similar problem, i a your solution but after testing i found that problem with connection is by missing entry in windows domain resolving file (hosts). After creating “ localhost” line flash debugger connects with “localhost” radio checked. But why debuggers worked before if there was not a line…?

  9. Max says:

    Interesting — I’m getting the same symptoms and have tried pretty much everything described in this and the prior article and still haven’t had any luck. I’ve got the debug player version 9.0.124 installed. Upon changing the debugger settings to my local IP address, I get the following alert from the browser:

    “A connection to the debugger or profiler could not be established by Adobe Flash Player 9”.

    Anyone else had similar issues? Suggestions?

  10. fabiopedrosa says:

    Thanks, same thing happend here.

  11. Not sure why that worked but it did. I’ve never had to click the “connect” at all before, but once specifying and it worked. Thanks!

  12. SOG knives says:

    SOG knives…

    Interesting ideas… I wonder how the Hollywood media would portray this?…

  13. […] this guy wasted hours finding a fix to this strange issue so I didn’t have to. Right click on the swf and click on “debugger” in the flash […]

  14. Muito obrigado!
    Você não sabe a que ponto minha paciência foi-se. Eu fiquei muito puto por nao saber o que fazer com este problema no meu flex builder 3. Os fóruns de flex aqui no Brasil não sabem de nada, bronca de sistema ninguem consegue resolver.
    Thank you so much!
    You don’t know how my patience vanished. I was really angered for doesn’t know what to do with this problem in my flex builder 3. That forums here in Brazil don’t know anything, a great system problem nobody can solve.

    Thanks again!

  15. Scott says:

    The problem I encountered is related to enabling the profiler. The solution was posted at and has to do with the PreloadSwf line in the mm.cfg file. Once I commented out the line the debugger worked as expected for both IE and Firefox.

  16. Annoyed User says:

    I’ve reinstalled the latest Flex Builder and flash debuggers, edited my config files, and opened ports all over and still profiler doesn’t work… really annoying.

  17. ::foogaz:: says:

    respect ünd thnx!! ;]

  18. I am using Flex builder 3 and Fire fox 3. When I tried to debug in Flex builder, the Fire fog pops up, but it’s not connected to debugger, do I need to install some kind of dll for Fire fog?

    Thank you for your help.

  19. Disgruntled says:

    I’m really confused because when I right-click “Debugger” is grayed out. Anything else I’ve found on this says that button isn’t even supposed to be available, but is simply there to let you know that you have the debugger version installed.


  20. JohanM says:

    Possibly your problem could be originating in the same issue that I’m writing about here:
    The bug tickets at Adobe and Mozilla is still open on the subject and hopefully they will be resolved soon.

  21. ChrisH says:

    Thanks a lot for posting this – since upgrading to Flash Player 10 and Adobe AIR 1.5, debugging stopped working, and others have had the same problems. Changing the IP address as per your description solved it!

  22. Gratus says:

    Thanks a lot for this post!!! I had the same problem one day at 1am – lucky for me after 30mins I found your post.

  23. […] but thank God it’s a 2 second fix ( I took the risk to burrow the images from the other blog: my saviour […]

  24. thanks dude…you saved my time i rather quickly googled my problem and voila!! i got to this page and problem solved.

  25. Paul says:

    WHOOO .. thanks for that .. i just spent half a day on this one, till i found this post .. the most annoying thing again, reinstalled fp 5 times, flex about 3 times .. was going nuts ! not a good start to the new year. Thanks once again.


  26. Bob says:

    Still having this problem after following previous suggestions. Any ideas?

  27. jason says:

    Debugger option is grayed out and not available so the fix doesn’t work.

  28. Scott says:

    Thanks for the solution. Debugger was broken from the minute Flex was installed on a new Vista box. Appreciate the insight.

  29. Adam says:

    Thanks!!! I’ve run into this issue dozens of times on a number of computers and never could figure out what to do. How stupid that works but “localhost” does not.

  30. RichClient says:

    Worked like a charm! How does it feel to have eliminated major frustration?

    Thank you!

  31. Ehsan Baghaki says:

    Thankx man!! I encountered the error and after just ONE search in google i found this and BOOM error fixed!! Thankx again

  32. Shade says:

    Hi, im using mac and doesnt work, any other solution for this problem?

  33. Mateusz says:

    Thanks! Now Flex Builder seems so much more useful 🙂

  34. pallzoltan says:

    thanks, very useful

  35. Tyler Gillispie says:

    Very nicely done! Solved my problem. I’ll never touch default settings again! 😉 –yeah right.

  36. Tim Symons says:

    Fix it for me too. This was driving me crazy since I was getting this error on XP at work but not on Vista at home!

    Thanks for tracking this down.

  37. Sid Maestre says:

    Thank you, thank you, thank you.

    I’ve been struggling, ignoring, returning to struggle more with this issue.

    Your solution fixed my problem. Mac OS X Leopard, Flash Debugger 9 and Flex Builder 3.2

    Thank for your taking the time to post it.

  38. matias says:

    I thank you very much!!!

    I had problems on Vista64, Flash Debugger 10 and Flex Builder 3.2

  39. […] After a couple of attempts of changing UAC settings, looking up ports etc I found a solution here. Basically what you need to do is specify where your application is running. Right click on the […]

  40. Lane says:

    billion thanks to you ..
    I stuck almost 5 hours

  41. junkoro says:

    I am going to shout from Tokyo, Japan. Thank you very much! It just worked!!

  42. iamconor says:

    Thanks for posting! It worked for me too!



  43. iamconor says:

    I found the cause in case anyone was interested. The localhost value in my hosts file had been corrupted somehow. I just had to set it back to and it worked with the debugger set to localhost or set to

  44. eme says:

    Thanks! It works here too!

  45. RaiulBaztepo says:

    Very Interesting post! Thank you for such interesting resource!
    PS: Sorry for my bad english, I’v just started to learn this language 😉
    See you!
    Your, Raiul Baztepo

  46. mpj_33 says:

    If the option for “debugger” is grayed-out, then double-check to make sure that you have uploaded the debug version of the Flex app, and not the release version.

  47. Tim Rowe says:

    The debug player I was using I couldn’t find a way to get that dialog up, and couldn’t get Eclipse to launch anything in a browser (only an Air app), so I’ve just spent half an hour trying to resolve the same problem, this was the solution for me:

    in hosts (\drivers\etc) localhost was bound to the ipv6 address ::1
    It seems Eclipse/Flash doesn’t recognize this, so I had to add an additional line for the IPv4 address, a line containing: localhost

    This fixed it straight away for me.

  48. Alex says:

    Champion! Thanks.

  49. wow thanks! never thought my problem would be as simple as this..
    now im back on track! thanks again!!

  50. SteveS says:

    I’m having the same problem and this doesn’t work me… because the Debugger menu item is grayed out in the context menu.

  51. Hmmm.
    Thanks BUT
    I wasted 2 hours on this problem and then I found your post.
    After making the change, it worked “like a dream”.
    Then it stopped working again “like a nightmare”.
    So, there is no solution for this.
    The community of Flex programmers is deemed to spend hours on the most basic of development functions – run the debugger.
    And you write you hate Vista?
    I admit I am a newbie outside of Microsoft, but its not a very encouraging entree into the world of Flash..
    Does anyone have any more ideas?

  52. Pierre says:

    I was having the same problem with launching an AIR APP in run and debug mode. I finally changed the application version in the
    your app name-app.xml file to:
    application xmlns=”″

    and all runs well in version 10

  53. tekkie says:

    It’s all very weird and most likely related to the hosts configuration file.

    But the thing related to it that I experienced with Flash Player Uninstall, is that it simply hung and didn’t uninstall a thing (on Mac).

    With every possible player-deploying thing closed, the only evidence of this piece of software (or shall I say crap) were 2 lines from the console:

    09.07.09 21:47:17 authexec[59427] executing /bin/sleep
    09.07.09 21:52:24 authexec[59458] executing /bin/sleep

    So pretty bad all this.

  54. Many thanks for Your post – it saved me today 🙂 I alredy spent several hours trying to resolve this strange debugger problem, but I would definitely spend another few before I found it out myself. Thanks!

  55. Sam says:

    oh my gosh thanks. I was able to find this post within 15 minutes of my issue and you probably saved me hours.

  56. Novian says:

    Has anyone figured out a solution for getting the Debugger to connect via either Firefox or Safari on a Mac OS X 10.4.11? I’m using Flex Builder 3 and I cannot make a debugger connection for the life of me.


  57. Mark Murphy says:


    If you selection “Other…” under the debug icon in Flex Builder 3 you can then add a “New Launch Configuration”.

    -for “Project” Browse to the project you want to debug.
    -Un-check “Use defaults” under “URL or path to launch”
    -for “Debug” browse to the .swf file of the namespace you want to debug

  58. z says:

    the orignal problem may couse of wrong setting in the file that hold all the hosts list
    (in xp – C:\WINDOWS\system32\drivers\etc\host)

    fix it may resolve the problem

  59. Aaron Nance says:

    Thanks for the solution. I should have thought of that on my own, but I didn’t so I’m very glad you did. I’ve had problems in the past with using “localhost” on Vista. They do everything IPV6 so localhost isn’t anymore, despite the fact that most applications still think it is. Leave it to MS to make something this simple so complicated.

  60. Pavan says:

    Hai sir
    The RiaFxZone site design is very good and attractive look and feel.
    I like those styles, effects very much.
    I am also a starting level flex developer.

  61. kirant400 says:

    Thanks a lot..

  62. jenue says:

    Hi y’all,

    I’m having issue while debugging flex app.
    I have this error message “a connection to the debugger or profiler could not be established by adobe flash player 10” when trying to debugger localhost. Is there any that i’m missing?

  63. Tomas Sancio says:

    I had the same problem with Mac OSX 10.5.8. Besides not being able to connect, my browsers would crash. So I uninstalled Flash Player using the uninstaller from Adobe with all apps (especially Flex 3) closed, then installed Flash Player Debugger version 10 from here and finally restarted my machine.

    So far so good.

  64. Kim says:

    For those noticing that the right clicking shows a disabled Debugger option- I simply went into my Flex3 application and under Player/MAC I reinstalled the Flash Player. Everything works again.

    (This was on a MAC – so PC persons might find their player elsewhere). Maybe this will help others.

  65. senthil.srinivasan says:

    thanks man great post keep it up !! hanks a lot …:)

  66. Andy Hudson says:

    I’ve been pulling my hair out on this problem for a few ours. Googled a lot, tried all types of solutions even uninstalling and reinstalling flex builder.

    Your fix was spot on! A big thank you for this post as it’s saved my hair (what’s left!)

  67. Joel says:

    Thank you so much! Saved me alot of hours of “debugging” this problem 🙂

  68. Bill Gray says:

    I know this sucka is old, but it just saved my butt! Thanks for leaving it up!

  69. Iftekhar Ahmed says:

    God bless you, it works.

  70. grammar says:


    I’ve had the same error for awhile now, but when I try to connect to Localhost it just does not connect. Same thing if I try “Other Machine…”

    Any ideas where I can take it from here?

  71. Robin says:

    Ok, here’s a trick for Mac users who haven’t solved this problem yet (and are using Chrome). First of all check if your browser is actually using the debug version of flash player:

    In my case it wasn’t after repeated un/reinstalls. However, in Firefox it was working. The problem lied with Chrome in my case. To uninstall the preinstalled flash player on Chrome go to /Applications right-click on Google Chrome -> Show Package contents. Go to Contents/Versions. For each version go down one level and remove the flash player plugin. Launching your flex app in debug mode shows that you’re missing the plugin. Download the debug flash player from the adobe site and voila, it works again!!

  72. Gertjan says:

    On OSX; I fixed my version of the issue by explicitly associating .swf files with “Flash Player”.

  73. Chris says:

    RESOLVED! Thanks for that tip! I had a localhost entry in my host file that redirected localhost to some other adress (for developement). I forgot that that was still in there! *Bang head against wall*. Thanks a lot!

  74. Andreas says:

    Thank You!!!!! Spent 30 minutes trying to figure this one out.

  75. Bob says:

    THANK YOU!!!!!!

  76. Best you should change the webpage title RESOLVED! Flex Builder 3 Debugger Stopped Working!! The World Wide Web According to … to more better for your blog post you create. I liked the the writing all the same.

  77. I had a similar issue which I fixed by upgrading to the debug version of flash player 10

  78. zinho says:

    Thank you so much !
    I try to install again and again flash debug and differents versions
    i try on various web browser, ie, firefox, chrome
    everything without success since two days…
    and i came on your site !!
    Alleluia, Mazeltov, Amdulillah !!

  79. Greg W. says:

    For what it’s worth, I too was experiencing the dreaded intermittent debugger fail using Flex 4 & IE. Would work fine three or four times in a row, then the next time the browser would come up with a blank screen and the debugger would not connect. The only way to fix the problem was to do a Clean… from the Project menu. At least on my machine, the problem was that occassionally when the system did it’s workspace build, it would automatically delete the swfobject.js file in our output (debug) directory. By just copying back a copy of that file, I found the application would run again just fine and no “Clean” was required. Had nothing to do with the version of IE, or the Flash Player (I was using the latest debuggable version the whole time). Still not sure why it randomly deletes the swfobject.js file — never used to do that.

  80. Denis Franze says:

    It’s not true! It works! I could reanimate my debugger! Thank you so much!

  81. ndc software says:

    It’s really a cool and useful piece of information. I’m happy that you simply shared this useful info with us.
    Please keep us informed like this. Thank you for sharing.

  82. Jyothi says:

    I am using Windows 7, flash 11, flex 3.6 version. When I open my application in debug mode, I am able to connect to the debugger. But it is not evaluating the expression. In Eclipse at the debug point it is showing the message as “An internal error occurred during: ‘Evaluating Flex expression’…java.lang.NullPointerException”. The application is working fine with out the debugger.

    Please help me to find out the problem. Thanks in advance

  83. Mark says:

    I get the same thing as Jyothi, you figure it out.., 2 days down the sink. Thanks.

  84. Mark says:

    Complete reinstall of FlexBuilder fixed it for me.

  85. Lalit says:

    Thanks a lot it worked … amazing ….. Thanks you once again

  86. druveen says:

    Brother Thankyou

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s