Have you tried to change the order of the databases that are being backed up ? If you have and still receive the error then you may have run into something that plagued us on a server for months on one seldom used server. Try having your network team replace the cables from your SQL Server to the switch and also on the backup target server. My guess is that you may have a bad cable.
RegardsRudy KomacsarSenior Database Administrator"Ave Caesar! - Morituri te salutamus."