Well, shoot. Sorry everyone, should have googled this a little longer before posting. I found confirmation that others have had this problem with large backups in compressed folders:

Thanks for the reply. If it helps anyone, here's the error message:

The process cannot access the file because another process has locked a portion of the file.

I know what...

The error message:

System.Data.S1qlClient.SqlError: File 'c:\Log\rp_log.LDF' is claimed by 'TransactionLog1'(6) and

'TransactionLog' (2). The WITH MOVE clause can be used to relocate one or more files.

Restore Database,...