This is happening to a number of people. Just please try to go back and use old - perhaps your original - UN and PW. It's worked for a number of people. If all else fails - we'll be able to link to back to your profile in the new system.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .