
Of course I shut down completely and rebooted...
Opened a version of the same session that had been backed up onto a different drive...
Tried different Autosave versions of the session, all crashed on Save...
...(but noticed that the most recent Autosave happened at the moment of the initial crash)
Noticed that Save As creates an empty 0 MB session file in the folder under a new name
(which gives you the "Unexpected end of file" error when you click on it)
Opened an entirely different session...
Disconnected entirely from my interfaces and drives and opened a session on the internal drive...
Result: no change. Sessions open, but when I Save or Save As, I got a hard crash of DP.
It seems that in the middle of a session, the Digital Performer application got corrupted somehow on the internal hard drive. Note: I was recording onto an external drive (USB 3.0).
I assume my next step is to reinstall DP, probably using the upgrade package to go to 9.12. But I thought I'd report my experience since I've never had an application be corrupted somehow in the middle of use. This may be some obscure OS X bug...