Take a look here, it may help:
http://support.microsoft.com/default...b;en-us;290684

"tk" wrote in message
...
I have setup a POP3 account in Outlook XP. When I click the test button to
test the settings, everything works fine. After about 20 minutes I start
getting a dialog asking for the username/password for the POP3 server.
Even if I check the remember password box, the dialog keeps popping up. I
have also checked the remember password box when I setup the account in
Outlook. Any ideas what is causing this?