Note: This is a vReveal 2 specific issues -- if you're running vReveal 3, it's unlikely that you'll experience this prroblem.

Some users reported problems with saving to H.264 MP4 format after upgrading to a new version of vReveal (2.2). This is typically followed by the message: 

"This file is either not currently compatible with vReveal, or it is not a valid video file."

right after starting the save to MP4. 

If you are experiencing this problem, make sure that there is exactly one instance of vReveal's H.264 encoder (filename h264Enc.ax) registered with the system. You can easily check this using Graphstudio (click on Graph/Insert Filter/Video Compressors).

If there are two or more instances of MotionDSP h264 Encoder in this list, please unregister them all (using a button on the lower right) and uninstall vReveal. Close and restart graphstudio and make sure that MotionDSP h264 Encoder is not in the list. Only then install vReveal again -- saving to H.264 (MP4) should work OK.

[Update: May 2011] This issue was fixed in vReveal 2.2.1. Vreveal 3 is not affected.