Oy vey ... Maybe it is a disk problem. The computer is relatively new. I just ran chkdsk and it found some bad sectors. I still can't delete the Calibre files although now it's a different error message (I need permission from SYSTEM to do that).
Yes, Calibre files are the only files affected that I know of, though this computer has a lot of problems running a range of programs that might be due to something like this.
It's a work computer for a rural nonprofit in remote Honduras, so getting things fixed is a problem ...
Any advice? I know it's probably beyond the scope of this site.