This started happening about 2 weeks ago or so...
We have the Family Pack Gold. I, as the primary member can log into Xbox Live fine. But all of my kids have problems logging in. When they go to access Xbox Live, they get a screen asking for the login info. They enter the main email address and password (for the primary account) and it rejects them. However, I can log in with this and I can also log in on a computer into Live with this info so I know that nothing has changed with my login.
I've tried clearing the cache, deleting the profiles and re-downloading the profiles but that hasn't helped.