Vista to Windos XP networking

I have been accessing a Windows XP server from a Vista system for several
weeks and yesterday for some unknown reason the XP server says that it cannot
log me on that my user name or password is not correct. I can go to the
server and logon with the same user name and password with no problem. I am
also able to use windows remote access to that same server with no problem.
As far as I know nothing has been changed. Other users using Vista can
access that same server with no problems. I also have Nortons Internet
Security installed and everything seems to be fine. Any ideas, I am out of
tricks.
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Gary L. Steward