What game are you trying to record? And what codec are you using atm?
I'm trying to record Battlefield 3 with it but the same happens no matter what game. Also, I am using the default codec because all the other ones that I have tried either crash the game or record at bad FPS.
Can you post a screenshot of your Movie Settings? You can use something like
Hmm I noticed it says 'Key Frame Rate: 0' and 'Quality: 0' whereas mine is 15 and 100, respectively.
Have you tried the 'Lagarith Lossless Codec'? It's one you have to download, which I am using.