All right, I win the total jackass of the month award. (Dwaine, you know for a fact I could never pass a sanity check.)
I just discovered that the damned drive in question (a 1TB SSD) was
full, and that's what resulted in that error message. Had no space for the database.
Now, what would be nice would be if the Resolve error message was rewritten to say, "Hey, stupid! You're out of space!" That would be a lot more helpful.
In the meantime, I'm setting this one on fire and getting a 2TB to replace it.
The backup now works fine with dashes. (Even if that were the issue, the error message should say, "hey, stupid! Don't put dashes in the file name!")
BTW, have I mentioned that I would really like to see an appendix for the manual that just listed all the error messages and possible interpretations of what they mean to humans? And could there be a Troubleshooting section, as in "if this happens, try X, Y, and Z?" That would be nice to have.