I'm moving my iTunes library to another computer that already had iTunes on it (both are Windows-based). On the original computer, video files loaded and played fine (I sync to an Apple TV). I tried to import video files that worked just fine on the original into the new one and they don't come over. If I copy the files into iTunes on a Mac, they work.
This ISN'T an encoding issue (I believe) as the files work properly on other iTunes. The only difference is one machine is 32 bit and the other is 64 bit.