backups getting code 71 "none of the files in the files list exist"

Hi

 we are having an issue with a client’s sever backup  that is consistently getting code 17 “none of the files exist”

In the job details “detailed status” window I see the following

Prepmspfvs1.   TRV – object not found for the file system backup: System State

(7108) System call failed – Connection reset by peer (at child.c.1298)

(7108) unable to perform read from client socket, connection may have been broken

(7073) Media manager terminated by parent process

(46996) Could not send server status message

Done.state: 71: none of the files in the file list exist

Hardware information

Windows server 2008 64 bit

Symantec netbackup client 6.5.2  ( I know we need to upgrade the client)

NBU master server is 7.5

Thanks for any help