I had the same thing happen a few times the other night. I also could not change my avatar. Turns out I needed to update my Adobe Flash. This new site is very heavy on the flash I have found.
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 .