Thanks for letting us know about this. Based on the error you are receiving, it sounds like there is a browser issue or process on your end that is interfering with the loading of the image selection pop-up window. I'm sure there are a variety of other possible causes as well.
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 .