Webmail username & password issue

[lamp]

Hello,

I'm running a FC2 server with the latest cPanel.

I have a user who cannot log into their webmail; even with the right username & password. The login prompt never disappears! I've even written a small html form for the user to have a different login method, but again, after clicking on login, the username & password prompt appears.

username: a@domainname & password: a <= can't get any simpler than that

Could this be an ISP issue? I've asked the user to try with different browsers but the same problem occurs.

Any thoughts??

Thanks.
Lamp

[sinfield]

Do you get the same result from primary account logins?

I am having similar problems, only with add-on accounts. Basically any login that requires the "@domain.com". And only for one domain.