The type or namespace name 'Mvc' does not exist in the namespace 'System.Web'

The type or namespace name 'Mvc' does not exist in the namespace 'System.Web' (are you missing an assembly reference?)

Solution: 

Clean your solution and then set the property of those references to Copy Local = True. If Copy Local is read-only, remove the reference and add it to the project again.

 

Copy Local = True