Sorry, I should have made it clear: I am *in* Quicken, using Quicken's Backup command.
Date and time added to the file name didn't work. Neither did trying different drives and different filenames. 20 minutes with Quicken Support also hasn't helped.
Later tonight I'm going to try 2 things: 1) going offline and turning off anti-malware programs (maybe they're locking the file) and 2) reinstalling Quicken.
Thanks for your effort, but we're done.
That didn't work either. Reinstalling Quicken didn't work.
But: under "File Operations," "Copy" successfully created a file that when reloaded seems to have all the information. I don't understand what's happening, but I don't have to. As long as that keeps working, I'm fine.