I haven't see this yet, but I remember that during busy periods of network between my workstation and NMC server I would get one of those using old NMC 3.1.

You can try :

setup -> system option :

unselect all :

Rpc ping via UDP
User authentification for networker
Networker user auditing

perhaps resolve your problem...

Last two have nothing to do with eventual timeouts while first one give you different kind of error if involved.