I was having a similar error with a WMV export. Just one sequence out of many that gave me a problem. It happened repeatedly about halfway thru, even after rebooting . I thought maybe its a particular shot in the sequence so I divided the sequence into thirds but each rendered suceesfully. So it wasnt that. I noticed something else strange in the process. When I defined the work area for the last third it consistently misinterpeted the area to be rendered to the whole sequence unless I moved the end point back by one frame. Hmmmm. On a hunch I added a second of black at the top of the sequence and a few at the end and voila! it all rendered perfectly. No idea what's really going on here but that worked for me. Good luck.