Rey Mysterio has been pulled from his June 03, 2012 appearance in Pennsylvania. Rey was going to be appearing at the Wizard World Philadelphia Comic Con alongside CM Punk, Melina, John Morrison and others. The information was available here. No word on who will take his place, if anyone does.
Also, on another sad note, Rey has also been pulled from his Japan tour set for this or next month. He was supposed to go on a media tour for WWE, but is now being replaced by Alberto del Rio.