well, i had a problem with an MS cluster once... clearly a network problem as the failover worked fine as long as you stayed in the same lan segment...
but the network dude would have none of it... so i ordered the cisco tac team, MS and compaq onsite on the same day... told em : deal with it.
Turned out the Cisco thing was ignoring gratuitious arp requests...
they swapped out one little daughter board, for another one that had the exact same FW and HW version.... and it worked...
Then i told em to send the 3 bills to the Network guy... that blew his budget for the next 2 trimesters