Can't receive mail

I have problems receiving mail. I've worked through the trouble shooting
guidelines and nothing works. I get a Windows Security box requesting user
name and password but entering the details doesn't fix the problem The
strange thing is that sometimes after I have gone in and reentered details in
the Accounts Properties - Server tab it will down load them BUT NOT EVERY
TIME. The Error message below is the most common one that I get.

Account: 'mail.bigpond.com', Server: 'mail.bigpond.com', Protocol: POP3,
Server Response: '-ERR [IN-USE] account is locked by another session or for
maintenance, try again.', Port: 110, Secure(SSL): No, Server Error:
0x800CCC90, Error Number: 0x800CCC92


Any ideas?????
.