I was having all sorts of difficulty in getting Sony Vegas Movie Studio to bring in the source files from my earlier http://TurnFunnyEMAILintoCASH.com video; it kept displaying errors about being unable to find certain files (despite that it did find most of them). I kept checking to ensure that everything had in fact come over when I moved my source files from the old computer to the new one; the main issue seemed to be that they used to live on E: and now they're on C:. The directory structure is identical, otherwise.
I finally found a single post that recommended installation of QuickTime; I did, and that worked. Very odd, but I think the base problem was that the software didn't know what to do with .avi files, but for whatever reason, thought that it was still trying to find files that had moved, and reported the errors as such.
OK, now let's rework this video to sell on Fivver! :-)