VS 2015 IntelliSense: Assembly Not Referenced Error

Question

I just switched to VS 2015. I have an older MVC 5 app that runs against 4.52. In VS 2013 it's perfectly fine.

In VS 2015 I'm getting red squigglies under my @Html.TextBoxFor() with an error indicating:

The type 'Expression<>' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

The project builds and runs just fine -- but I am concerned about the IntelliSense error that never happened in VS 2013. Okay, so I try to add the reference to System.Core as recommended in the error above and then I get this error:

A reference to 'System.Core' could not be added. This component is already automatically referenced by the build system.

Again, this is fine in VS 2013.

Answer 1

I had the same issue, but in the mean time I've found the answer:

I had to add the following references to my web.config (add inside the opening system.web tag):

<compilation debug="true" targetFramework="4.5">     <assemblies>                 <add assembly="System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>                 <add assembly="System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>                 <add assembly="Microsoft.CSharp, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>                 <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />                    <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />                 <add assembly="System.Web.Helpers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />                 <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />                 <add assembly="System.Web.WebPages, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />                 <add assembly="System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />             </assemblies>         </compilation> 

I also changed the target framework from 4.5.1 to 4.5.

p.s Close and reopen Visual Studio after changing it.

Answer 2

I have tried most of these, what eventually worked for me was unloading the project, edit the csproj file, and add the following:

<Reference Include="System.Core" />