Windows Mail And Outlook 2007 :endless "verify User Name And Password"

I'm trying to set up Windows Mail and Outlook 2007 to use an email box in a new website. I have two email boxes with different passwords on the same site. The first account in Windows Mail worked... but the second, set up the same way, will not. I get repeated Windows Security dialog boxes with "verify user name and password" until I cancel the dialog which returns the following error:

Account: 'mail.mysite.org (1)', Server: 'mail.mysite.org', Protocol: POP3,
Server Response: '-ERR authorization failed', Port: 110, Secure(SSL): No,
Server Error: 0x800CCC90, Error Number: 0x800CCC92

I'm using Vista 64-bit which has always been exceedingly careful about what programs it will allow to run... but the places to adjust that are obscure. Is the problem in Vista-64 security setting? Turning off the Norton Internet security makes no difference. If I import the one account that works in Windows Mail into Outlook 2007 (and check that all of the settings are correct) it doesn't work in Outlook. The same endless Security dialog occurs.