Many a times we get this error message saying flex-debug not found and won't launch the debugger.
The solution which I found is first get the flash unistaller, and then install the debugger version of flash player, it will start working as before.
The link for the flash uninstaller is as below
http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html#main_Download_the_Adobe_Flash_Player_uninstaller
One its done, installer the debugger version which you can find in the link below:
http://www.adobe.com/support/flashplayer/downloads.html
This shall sort out our issue of the debugger not getting launched.
