Back in the early days, RAM was checked (very slowly) before the underlying DOS handed over to Win. So I'm surprised RAM isn't checked, but if not, then TS is likely right. Certainly it's a cheap fix to reseat those modules; just make sure you are earthed to the case before grabbing them.
What I'm still not clear, is OP says Vegas works OK except with this Project, so doesn't that point to something in this project. However, it would be interesting to create a larger project "Project Bigger" which would exercise the RAM and everything else, in case it's a throughput issue. However, I'm sure there are RAM-test programs, but maybe someone here can say if RAM is not tested at the start?
Now this Project:-
back to that "red file" - Isn't the easiest thing, is remove it and replace that "time event" with another file of the same length. If this "replacement" doesn't turn red, this points to the original clip having a fault....you could try cutting it in half to see if the fault stays with the start, or finish, - if it does then you might be able to shave-off a bit and save the day.
A little frustrating that he never came back to explain if it was a corrupt file!