I've rendered several videos into the .mp4 format. But all of a sudden now, when I select the Main Concept AVC/ACC (*.mp4) as the output format, the description in the Render dialog box says "No existing templates support this media". I was able to render several videos in this format just this morning, but now I can't. On top of that, when I drag a .mp4 file to the timeline, only the audio portion of the file shows up -- no video. I can play the video file just fine by double clicking on it in Windows explorer, where it plays with Quicktime. But I can't play or edit it in Vegas.
I've removed and reinstalled the software (Vegas Movie Studio+DVD Platinum Edition, v7.0a) and I'm still having the same problem. Suggestions for how to fix this problem would be greatly appreciated.