In case it happens again, these lines in the messages
BusyError: BusyError: database is locked
suggest something is holding a file lock on the calibre database.
If you logoff/logon to Windows that may fix it (it did), if not its probably something like an antivirus scanner, you could try excluding the calibre library folder from your AV program.
Otherwise use the "How to find out which handle or DLL is using a file" method in here ==>>
How to Find Out Which Windows Process is Using a File
BR