We can't know anything without some system info, but as a start you might do a search on this forum. This has been discussed several times. The long and short of it is, that either your Fraps settings are unsuitable and produce incompatible output or that you have made a mess on your system by installing CoDec packs. Adjust your recording settings, get rid of garbage liek K-Lite or whatever, reinstall AE...
I use windows 7, the 64-bit version and I use 29.97 fps on fraps and on AE. I have never installed CoDec packs and i don't even know what those are. same story for K-lite. the program i usually play my videos on is Windows media player. by the way i haven't seen any discussions on this topic. the weird thing is that other videos do work, it is just fraps. but I don't think there is anything wrong with my fraps settings.
i use After effects CS6...
Could this be the problem? I quote from the FAQ at the Fraps web site:
"Where can I find the custom Fraps FPS1 codec?
The Fraps codec (FPS1) is put on the system when you install Fraps. If you've reinstalled Windows you will also need to reinstall Fraps in order to play back your movies.
Please keep in mind that if you want to give your raw footage to another person they will also need to have Fraps installed."
Come to think of it, spending some quality time with the Fraps FAQ's for a little troubleshooting work might solve all your problems... because you're only having trouble with Fraps, y'know.
thanks for the help, it is true I there is a problem with the codec because I can't find it anywhere. I've sent an email to the fraps service. all I can do for now is just wait. after I've re-installed fraps I still didn't have the codec so that is very strange.
problem solved, the problem was apparently not the codec, but the file type. I converted it into an mp4 file and it worked. thank you both for your effort though.