It looks to me like Vegas is waiting to rewrite that part of the screen. Either another task is higher priority briefly, or Veg is waiting for some service to be completed, perhaps a fetch from a disk or somesuch.
I get the same thing with Vegas 12 now and then, but it produces the Vegas "do you want to send an error report" process and locks up completely. I use Windows task manager to shut it down. Weird thing is, although Vegas is locked up, you can still 'save' before closing it. Takes maybe 3 hrs of editing to happen.
OK. I have my files on a separate network drive so maybe that's the problem. Next edit I'll copy the folder contents onto C Drive and work from there. Thanks for the idea...
My source files are on a separate internal drive. I have a C: (system drive) plus an internal for source files, and another internal for rendering to. Have been working this way since the stone age. :-) Actually, I don't ALWAYS get the Vegas crash dialogue, mostly Vegas just sits there locked up (apart from 'save'). I've tried previously leaving it for 10mins or so, but got no change.