Was there an error code at the end of the message?
Usually there is and it will help in tracking down the source.
It would help if more data was supplied, for example:
name of backup program - ARCserve, BAB, BEB
version
how often does it happen
does it happen with each volume
how much data is backed up before it happens
Usually it is a problem either over the network or at the remote system end. I'm not up on this agent, some of the others support specifying a specific IP address (in case there are two NICs you can have it use the other), setting backup priority to low. Make sure the NICs are configured for a set rate rather than autodetect, and it is correct for the port it is plugged into. Logging at the switch or via a network monitor will help to identify if there are problems on the network.