Mail won't hold password

[David Tinker]

List

My ISP recently upgraded their server, and, bad luck, I upgraded to 
10.2.3 at the same time. Now, whenever I get mail, I get a window 
saying the mail server refused my password, please re-enter. Meanwhile, 
the mail is being downloaded in the background.

If I enter my password, downloading stops for a few seconds, and I get 
another window with the same message "the POP server at 
you.yoursite.com has refused the password....." and downloading 
continues.

I have administrative access to my POP server and I  have reset 
passwords there, in Mail prefs and in internet prefs, but still it 
continues.

10.2.3, Mail 1.2.3

Any thoughts?

Dave Tinker