We're using WSS v.2 which causes a regular issue to some of the users only but that is extremely frustrating.  What happens is when they work on a document with the document being open for a period of time or the user leaving the desk to go to the meeting with the document left open, when they get back to working on the document they're asked for authentication when normally they do not need to get into SharePoint in the first place.  Having entered their correct user name and password the authentication window pops up for 3 times and then they get the view "you're not authorised to view this page".  Please note that this page is different from a standard view when a user indeed is not authorised to access the site and where they need to request access from site administrator.  We have investigated the set up on the PCs that these users are using and didn't see anything apparent differences from the set up of the users who are not experiencing this issue.  Does anyone know what could be causing it??

Thanks!