I also get this Vegas crash error after closing some projects. This has happened for a few versions now. I have Win 7 x64. Just wondered if it's a windows problem rather than something to do with Vegas? It doesn't seem to effect my projects at all but it is irritating.
I have had several freeze's using Pro 13 now including the error message when i have shut it down at the end of an editing session. They appear to be random, although usually occur when moving media around on the timeline, or during playback on the timeline. What graphics driver is everyone using (335.23 for me on a GTX 670 card). V12 has been working pretty much uninterrupted with this configuration.