UVS 11.5+ fails to combine video and audio

[sclgwhite]

After performing flawlessly for several weeks, the editor will not combine an audio-less video with a .wav file in the audio channel. I started with a .mov video, but have converted it to other formats trying to get it to work. Most of the time it processes 99% (exactly, every time) and gives me "sorry we have to close, hope you weren't in the middle of something", but I can start with the video (no audio) in .avi format and get through processing it with the added .wav file; however, the product is a video file with both extension .mpg and .mpv, plus an audio file with both extensions .mpg and .mpa. Neither file will play as is, but removing the .mpv extension allows the video to play with sound. I rejoiced when I discovered this, but my joy was dashed when I trashed the .mpa file and found that the video has no audio. Somehow, Windows Media Player can play the audio when the .mpa file is in the same folder. Have any of you experienced this craziness? After 4 days, I have exhausted my ideas.
Sid