title: System.core dll can not be referenced
body: <p>I am trying to solve Dlls reference problem in Visual studio 2012. All dlls have set them self in a way they are looking for .net 4.0 version while I can not install because i have already .Net 4.5 installed with Visual studio 2012.I have asked <a href="https://stackoverflow.com/questions/18405973/net-4-5-system-dlls-are-missing-after-installing-windows8-sdk-and-restart">this Question</a> </p>
  
  <p>but I didnt get a proper answer.Now I am trying to reference System.Core in 4.5 but it can not be referenced as visual studio  is not allowing me to do, it says it will be referenced automatically during project build but actually it does not.I am in catch 22 situation.Kindly advise.
  I have reinstalled Visual studio 2012 but it didn't help.</p>