Constantly asking me to Login...

We have a few PC's that access the helpdesk software that is run on a server, these have been running fine for the last two week, but we have updated 2 of these dekstops using windowsupdate.com, and have mae sure that all available updates have been installed, since then we have the problem where when you try to access any page or link in the helpdesk software you are asked to re-login, the systems are Windows 2000 SP4 and Windows XP SP2, they both have Mozilla Firefox and IE and the problem is seen in both browsers, the other workstations are running fine, and do not see this error, I have tried various settings in IE and Mozilla but can not stop this annoying thing from happening, anyone have any ideas as to a work-around.