Outlook 2007 asks for password upon opening

"Does the problem persist with a fresh profile, configured with the new credentials?

You may also have an incorrect password saved in your saved passwords. You can manage your stored passwords from Control Panel -> User Accounts. (I believe the process is slightly different under XP and Vista)"

"This may be a Windows security issue. If your (old) password is stored somewhere else (maybe a Windows Service running under your account or a connected network share on another machine) where an automated login is configured, after a certain treshold of failed login attempts, the server asks for password every time on other automated logins. So, this will affect your Outlook login, even if the password you insert for the login is the right one.

This behavior is known - probably not in your case - wenn a virus attemps to crack password sending login requests to your server, like the Confickr worm does."