How do I solve a problem with XviD?

I have been trying to convert some movies to iPod format and have downloaded (and then quickly deleted) quite a few programs that didn't work for me. Now Vista is telling me that there's a problem with XviD and I don't know how to fix it. I have already gone through the process of uninstalling the programs and it didn't solve the problem. Has anyone managed to fix this?
Okay, fingers crossed, I think I have it worked out. Apparently whatever was causing the problem was in the Recycle Bin and when I emptied that, the message stopped popping up.