Can any of you network gurus help me out with a TSM problem?

We currenty have an isolated 100mb ethernet network for TSM.
We have three NICS in the TSM server, each attached to a seperate V-lan
We spread the servers backing up across the three v-lans

We are having on clients on one of the vlans that intermittently get
"session lost re-initializing messages" in the dsmsched.log

When we ping the clients from the TSM server we get no seesion or packet
loss

When we ping the TSM nic from the client we get intermittent packet losses

We replaced the NIC in the TSM server
We replaced the cable from the TSM server to the switch
We replaced the cable from the client NIC to the switch

We've ensured that both NICs are set to 100/full

My network guys are out of ideas any body have any suggestions?