Are you sure the client doesn't have a compromised Windows box somewhere on
site spewing out rubbish every few milliseconds on 135-139 looking for other
machines to infect?

There have been a few occasions where I've had firewalls stop accepting
connections for seemingly no reason and it's been traced down to a client PC
clogging up the state table with millions of entries as it looks for other
victims.

Regards,

Chris
-- 
C.M. Bagnall, Director, Minotaur I.T. Limited
This email is made from 100% recycled electrons