There can be other causes of this message, such as preemption by higher 
priority tasks (particularly restores, retrieves, and recalls). See what the 
server Activity Log contains at the time that the client encountered its error, 
and examine the log prior to that for resource consumption (drives, etc.) by 
other sessions or processes leading up to the problem for the affected backup 
session. If you are using disk storage pools for arriving data, insufficient 
sizing can result in filling and then an elevated demand for tape drive 
resources and thus contention and delays. I would also inspect the client logs 
to see if client processing got mired such that even a 60 minute Idletimeout 
would have been exceeded.

    Richard Sims