Cannot Get Second Email Account To Work In Windows Mail

I have just transferred from a Windows XP PC using Outlook Express 6 to Vista PC with Windows Mail. I successfully migrated one email account and it works fine. On a second account I get the windows security box asking for username and password and even when I enter them correctly I get the box again. When I cancel I get the following error message:

Account: 'Estradia general', Server: '127.0.0.1', Protocol: POP3, Server Response: '-ERR unknown user name or bad password', Port: 110, Secure(SSL): No, Server Error: 0x800CCC90, Error Number: 0x800CCC91. However the username and password are correct, and the account does send and receive emails OK. The account is located with the same ISP as the fully functioning account. I have checked that all the settings etc for the caccount are correct, and have tried manually inputting them with same effect.