I also have yahoo toolbar and it doesn't give me any problems. However the toolbar does have a popup blocker option, which WILL give problems if enabled, that may have been the problem.
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 .