Cannot sign in to Family Safety with existing Microsoft Account

I cannot sign into Windows Live Family Safety with my existing Microsoft Account.

I enter the email address and password, and click the Sign In button, then get an error message saying "The email address or password is incorrect".

1. This happens on two different Windows 7 laptops. I have rebooted, cleared history, etc and this has not helped.
2. I have checked the email address and password numerous times (case is correct, Caps Lock is not on, etc).
3. My email address/Microsoft Account is not an Outlook.com, Live.com or Hotmail.com address - it is my own domain, something like <*** Email address is removed for privacy ***>
4. The Microsoft Account works for all other apps and web sites on my Windows 7 laptops, Nokia Lumia 920 phone, Lenovo ThinkPad 2 tablet (Win8).
5. This Microsoft Account <*** Email address is removed for privacy ***>works for Office 365 Home Premium just fine.

The email address and password are correct, so why can't I log in? I used to be able to log in OK.

Thanks