The current versions of ASP.NET now only support full trust. MS have stated in Release Notes: Known Issues that:
ASP.NET MVC 5 no longer supports partial trust….
In particular the [assembly: AllowPartiallyTrustedCallers]
attribute has been removed from the source code. You can read more about ASP.NET’s official position in Levi’s answer to is-trying-to-develop-for-medium-trust-a-lost-cause, which also includes further links to why support has been removed.