Unexpected file format

hi everybody,
I have huge problem with my Flash MX 2004 Proffesional and with all other flash versions.
The problem is : I work with Flash MX 2004 PRO, but when want to open a *.fla file that isnt created by me.... let me say, that my friend who is using the same version of Flash, creats a simple *.fla file.. then he send it to me, and when i want to open it i cant… My Flash shows this message : “Unexpected file format” ! I tried to uninstall the Flash and then again install , but the problem appears again! I tried with the older version - Flash MX, with it i can open most of my *.fla files, but i can`t open the files that i created on Flash MX 2004 PRO, the same error appears “Unexpected file format”

I tried to format my C drive where my Windows is located but the problem still exist!