I found a suggestion in another debugger problem thread to run a Flash Player installer from within the Flex Builder folder. I found an app named "Flash Player 9 Silent Installer.app" and ran it. My debugging functionality is back now, but the player version is a lot older.
The only culprit I can think of for this problem is Firefox. I recently upgraded to v 3.5.3 and I remember it popping up a warning about Flash Player needing to be upgraded immediately. I wonder if it overwrote something that caused this?
Can someone at Adobe please attend to this , I have the same problem on FB3 and its an ongoing issue on forums. Please please help, I bought FB3 in good faith and it isn't doing what you guys said it would
I was getting the same error message, but I was still able to debug and see trace statements in the console. I found that I get this error message whenever I elected not to generate an HTML wrapper (Project properties > Flex Compiler > Generate HTML wrapper file).