Created Unassigned: After upgrade from MVC 5 to 5.1 Could not load file or assembly could not load 'System.Web.Http, Version=5.0.0.0' [1662]

As per title,
I have upgraded from MVC 5 to 5.1 and receive this error

Could not load file or assembly 'System.Web.Http, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Ive tried copy to local, and adding the dll manually from the bin folder but no luck.