Cannot determine status of probe process - backup fails

If someone could help me with this one you would earn guru status. I have a call into EMC support but they have not been able to solve it.
One client is a new install of XP and has always failed with the following messages (in verbose savegrp mode):

"Cannot determine status of probe process. The log file is empty."
"Probe unexpectedly exited."

I have (sucessfully):
- turned all firewalls off
- uninstalled & reinstalled the client
- Checked client res/servers files for backup server name
- Checked name resolution (it's fine)
- rpcinfo -p reports nsrexec running (both ways, client & server)
- recreated the client entry in NMC
- client PATH env variable is good
- deleted the NSR Peer info

The network connection goes through one switch and the other clients backup fine.

I am at the end of my rope short of reformatting the drive and starting over.
Any other sane ideas?