Copied from the Xbox site at this url:
Xbox Live Access Messages
"Users may experience difficulties with account recovery, account management, Marketplace functions and/or making purchases. We are aware of the problem and working to resolve the technical issues. We apologize for any inconvenience this may cause and thank you for your patience.
Users will be unable to log in to Xbox.com or access the Marketplace on Xbox.com. Users will also be unable to post to Xbox.com forums. We are aware of the problem and are working to resolve the technical issues. We thank you for your patience."
Hopefully this explains why I was unable to add points earlier this afternoon.