Not able to add class library dll to Windows Phone 8

问题

I can’t see the unblock button and the same means its already unblock to use,right! but i’m not able to add the class library reference to my Windows Phone 8 application and error ‘A reference to a higher version or incompatible assembly cannot be added to the project’ appears. Please help me out!

来源：https://stackoverflow.com/questions/15377890/not-able-to-add-class-library-dll-to-windows-phone-8