Joe, Thank you for your response.
We know about the .old etc. It almost never works. Plus, as I said, we do have a workaround using File > Restore as noted. It's faster to delete all files and do a clean Restore if we are sure we have things backed up. But I'd like to know what is causing the problem and how to prevent it from happening.
Can you or someone else please answer the key question:
What is the message for? Is it telling us that QB wants to Run File Doctor and clicking Start would do that? Why doesn't it say that instead of displaying cryptic ASCII text? Is there some way we can fix that cryptic message so it displays correctly? BTW, the text it displays is not the same every time. And this happens on multiple companies not only one or two, so I think something else is not right.
What other things can we try that might fix this kind of error?
Thanks again for your help.