Opening an older version is a good idea. Make use of your attic anytime you think something has gone corrupt.
I would usually start by deleting my media databases and even my MCState setting file. It’ll rebuild when you relaunch.
Rename your AvidMediaFiles folder to something else to put all your media offline…do you still get the error?
If it is a piece of corrupt media, on your timeline, not only can you try to narrow it down by playing your tracks out individually, you can set in and outs on the track and doing a “play from in to out” Mark an in at the head, and an out in the middle, and play from in to out. If the corruption remains, mark your out 1/4 of the way through the timeline. Keep doing this until you track down where the corruption ends. I’ve used this method to find bad media in the past (and corrupt title files)
If corruption still exists, open a clean project and bring bins from the corrupt one in, one at a time to see if you can find the corruption. This may tell you if the problem is the project, or a bin within the project.
If you have access to another computer, load AVID on it, and open the project on it (sans media) to see if the problem persits.
Troubleshooting is always fun.
Glenn