In addition to Phil's response, on heavily used networks there can be the issue of port exhaustion: since most people also run DNS services on the domain controller, busy systems can actually use up all 65,535 ports. I've seen this several times, and unfortunately nothing can be done except for offloading the DNS traffic.
EDIT: Or, of course, give DocuWare its own server as suggested!
Software Support Specialist
Support Team GREEN - Americas