In my Previous post when you encountered this error “The Security validation for this page is invalid.Click back in your web browse”, turn off the security validation of the page so that it wont show you this error, but the flip side of this, when ever you are going to create the List, Library from the gallery in the SharePoint website, you will encountered with this error “An unhandled exception occurred in the Silverlight Application”, now to avoid this revert back to same setting in the Central Administration.