I have run into the following problem several times recently. I opened a file to look at it then closed without saving. I get this error message:
It has ever caused a problem before but today, I went back to the original file and it was totally trashed.
You can click yes or no until you get into the file.
Then use the File > Revert to… tool to roll back to a previous version before the problem.
The revert shows two versions, both of which are hosed.
The file opened fine originally. When I tried not to save, I got that error message and I now get that error when I try to open the file (and Rhino crashes).
I’m on the road but I backed up right before I left. I pray the file is there on the backup and functioning when get back. Most likely no disaster.
As I said, I have seen this error message before but I was always able to open the file afterwards with no problem.
The Mac file system is great until it isn’t.
It’s ALWAYS smart to have a Time Machine backup setup for just such situations.
I’m not aware of anything else that is reliable.