Please provide more information, attach the detailed status log. Please provide the OS, Master/Media/Client?

This could be of couple of reasons.

N/w utilization, issue on client, tcp chimney offload settings

Does it write a bit and fails? If other backups in the environment failing with same error look for the n/w utilization and issues in the n/w. If only backup fails for this client with this error check the n/w settings on the client itself.

bpbkar on client, bptm on media server will help!

Server 2008 Enterpirse Edition /Master Version 7.0.1 / Client OS - Server 2008 Enterpirse Edition

On that time some of other backup was running and completed succesfully.

Please answer all questions in sazz's post?

Such as all text in Job Details tab; is any data written before it fails?

All logs mentioned in sazz's post as well as bpbrm on media server.
Please rename logs to reflect process name (e.g. bpbkar.txt) and post as Fille attachments.