ReadyNAS 2120 Freezing with multipul concurrent connections

This is a brand new unit, I have one share that I'm using as a backup location for disk to disk backups. We use CA Arcserve 16.5 D2D, if I have more than 3 jobs connecting to the ReadyNAS at the same time the box becomes unresponsive causing my backups to fail. This happens EVERY time. I tried using SMB shares, NFS, and iSCSI ... same result. When the box becomes unresponsive, I can still ping the NICS but I can't browse shares or the web interface. After a manual reboot, everything is backup and running. I've also tried bonding the NICs, and using both nics independently and distributing the jobs over both nics. Nothing seems to make a difference. It's almost as if i'm saturating the hard drives while writing and this locks up the unit.

Anyone have any ideas?