I believe the problem is due to the ~ in your user name. Ironically, we've just disabled the ability to register IDs with ArcGIS Online with user names that contain special characters. You got in before we made the change.
User names can only contain letters, numbers, underscore, dash, dot, and the at sign.
Unfortunately, it is difficult for me to reproduce as I can't register such a user name myself. My recommendation is to create a new user name and use that one instead.