using a 5TB NFS share on an iOmega StorCenter px12-350r

import of VM goes without a hitch  but attempts to start the VM result in:

SNFS Stop [ OK ]
[FAILED]
sd 0:0:1:0 timing out command, waiting 360s
end_request : I/O error, dev sdb, sector 0
Buffer I/O error on device sdb, logical block 0
etc to logical block 9

ideas?

thanks
Martin