Ok, after 6 and a half hours of fun I have discovered that the reason for this is due to fonts problems, I had removed my fonts from font agent pro although not from font book..
To see if this problems is what you are having:-
1) Boot up your mac in safe mode (hold down shift immediately after you hear the startup chime) This disbles all fonts
2) Open flash and your problem file (files) or any (fla) file really to check it doesn't crash
3) If flash opens successfully and the file opens showing a missing font dialogue box, you have the same problem..
4) If this is the case reboot..
5) Remove all of your own fonts from your font application (Suitcase/Font Agent Pro)
6) Remove all non system (user) fonts from Font Book (make sure to back up your fonts first as this erase them of the system)
7) Delete the flash preferences (com.adobe.flash-10.0.plist) file located in (user)/Library/Preferences
8) Relaunch flash
With a bit of luck... problem solved !
I hope this saves some other poor soul who had been looking forward to updating their website whilst off work to not waste 6+ hours sorting it out..