I had this happen with a project once. It did not involve video. It
seemed to relate to corruption caused by my pulling a large number of a combination of stereo and mono one-shots into a mono audio track. What I did was return to a previous version and re-pull each one-shot into the track, one at a time, saving each time. At some point I'd get the general error, go back to a previous save, and continue. Eventually I "cleaned" the track and stopped getting the error.
What might work is to copy all, open up another project, and paste into it. Try saving. If that doesn't work, you need to find out if something in a particular track is causing corruption. Again assuming you can copy from the project, eliminate tracks one at a time in the copy and see if you can save. If so, then you've found the corrupt track.
This is all very "shot in the dark" but hopefully this might give some kind of a clue. It is very frustrating as there is no real indication of what the problem is. To Bob's point, though, I was running low on hard drive memory so maybe that's another clue.