You know you were using a password. While you remember it, write down your password. Don't change it.
You probably were using a "Live ID" which involves an email address and a case-sensitive password. Here is how to deal with it:
Disconnect from the Internet. Start Money, and log in offline.
Remove your LiveID. Do not attempt to change your LiveID. If you
already changed your LiveID, use the credentials that were in
effect at the time that you saved that Money file.
To remove the Live ID in Money 2006 or later, go to
File-PasswordManager, and choose to remove your LiveID. To remove
or add a conventional password, also see File->PasswordManager.