I am having this problem as well. I bought the 343 a few weeks ago and I put 160gb drives in it at work and messed around with it*. It seemed stable and I took it home this week to plug my 4x1TB drives in and after creating the raid, any sustained copy to this unit bakes out with the windows error..
Cannot copy <file>: The specified network name is no longer available.
I have changed ports, switches, patch leads etc to no avail. I have tried this in RAID 5 and RAID 1 and same result. ext2/3 same result. If anyone else has had this issue I would love to hear about it, because its sounding like a faulty unit at this stage.
Running firmware 1.02
-Dan
*Note I didnt try copying more than ~1gb to it at the time.