Disappearing User Profile

I have an issue here at work where there users that keep losing their profiles on XP pro(by saying losing their profiles I meant that it is like they have never logged into the machine but under user manager they remain there). The only thing in common is that I have removed Norton, added CA Etrust, and made it so that their My Documents Folder is saved to a Network drive. I am on a domain with active directory. Servers are running 2003. It appears to be only the same 6 people that this happens to. Any help would be greatly appreciated.