Waiting for Adobe Flash Player to connect to debugger
Recently a FlashBuilder project I was working on just stopped compiling using the debugger. The program would just hang with the build progress stuck on 57%. I tried many things to fix this, including uninstalling and reinstalling the debug versions of the Flash player without any luck. Eventually I found that the player that was launching was not the Debug player but the Release build. I discovered that once I changed the file preferences for SWF files it would debug again.
To do this on a Mac, select "Open with...", choose "Other...", select the Debug player and check the "Always Open With" checkbox.
There is another method document on StackOverflow that I haven't tried.
Mac OSX / FlashBuilder 4