ZT From:http://leopowerword.javaeye.com/blog/341339
Installed Flash Player Is Not a Debugger
C:/WINDOWS/system32/Macromed/Flash/Flash10a.ocx
Flex Builder cannot locate the required debugger version of Flash Player.You might need to install the debugger version of Flash Player 9 or reinstall Flex Builder.
Do you want to try to debug with the current version?
Download the Windows Flash Player 10 ActiveX control content debugger (for IE) (EXE, 2.03 MB)