The 11 digit, all numeric id is obsolete but some parts of the system will still take it -- it could disappear anytime.

The 8-char MP account id -- starting with 2 or 3 chars -- is the official account id.

Other older usernames or emails not longer work.

Does the 8-char MP account id not work today?
Are you sure you have the right account id?

Works fine for me.

every so often, the logon proceedure does not work for a short bit. rare and it corrects itself in minutes usually