Domain user periodically can't login, but only temporarily?

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http://serverfault.com – Ok, this is a strange one that I'm having trouble replicating letting alone solving. I have a user who uses two computers (both XP sp3) on the domain with a roaming profile. She has no problems on her personal computer but occasionally needs to use a shared computer. On this shared computer she is sometimes (~once a week) unable to login with the error message "Username or password incorrect. Check username password and domain and try again." I've checked when this happens and her username and password are indeed entered correctly. Now the strange part - if someone else logs in to the co (HowTos)