event id 529

i have two nt4 sp5 workstations generating event id 529 errors in the security log as soon as they start up…the users are able to log on as normal and there do not appear to be any other ramifications…in fact nothing untoward at all is happeningexcept the log is full of just these errors..it is only these two machines out of 40 clients…
i could of course disable auditing on these events but that doesn’t really cure whatever is going on….it happens with any user so it is definitely a machine rather than a profile or user issue…technet is no help and i’m stumped….help

thanx

bob