Vegas 6 renders vanishing
 

I just started having a problem when rendering (60-90 minute) mpeg2 or avi files using v6e. The renders begin OK and the process continues all the way through - I can see the "rendered" file in the designated folder, BUT once the render is complete the file vanishes. I have done a search to see if the rendered file was moved to a different location, but no luck. Shorter renders are OK. Any thoughts?