[c#] Build error: You must add a reference to System.Runtime

I'm preparing a brand new ASP.NET MVC 5.1 solution. I'm adding in a bunch of NuGet packages and setting it up with Zurb Foundation, etc.

As part of that, I've added a reference to an in-house NuGet package which is a Portable Class Library and I think this is causing a problem on the build server.

TeamCity fails the build with:

The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0

I originally added the fix for the same or similar error when compiling the Razor web pages, that fix being in the web.config

<compilation ... >
  <assemblies>
    <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
  </assemblies>
</compilation>

However, the issue is unresolved.

i added System.Runtime.dll to bin project and it worked :)

Removing the reference over the Nuget Package Manager and re-adding it solved the problem for me.

I had this problem in a solution with a Web API project and several library projects. One of the library projects was borking on build, with errors that said the Unity attributes weren't "valid" attributes, and then one error said I needed to reference System.Runtime.

After much searching, reinstalling the 4.5.2 Developer Pack, and nothing working, I figured maybe it was just a version mismatch. So I looked at the properties of every project, and one of the very base libraries was targeting 4.5 while every other one was targeting 4.5.2. I changed that one to also target 4.5.2 and the errors went away.

It's an old issue but I faced it today in order to fix a build pipeline on our continuous integration server. Adding

<Reference Include="System.Runtime" />

to my .csproj file solved the problem for me.

A bit of context: the interested project is a full .NET Framework 4.6.1 project, without build problem on the development machines. The problem appears only on the build server, which we can't control, may be due to a different SDK version or something similar.

Adding the proposed <Reference solved the build error, at the price of a missing reference warning (yellow triangle on the added entry in the references tree) in Visual Studio.

The only way that worked for me - add the assembly to web.config

<compilation debug="true" targetFramework="4.5">
  <assemblies>     
    <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />   
  </assemblies>
</compilation>

To implement the fix, first expand out the existing web.config compilation section that looks like this by default:

<compilation debug="true" targetFramework="4.5"/>

Once expanded, I then added the following new configuration XML as I was instructed:

  <assemblies>     
    <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />   
  </assemblies>

The final web.config tags should look like this:

<compilation debug="true" targetFramework="4.5">
  <assemblies>     
    <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />   
  </assemblies>
</compilation>

@PeterMajeed's comment in the accepted answer helped me out with a related problem. I am not using the portable library, but have the same build error on a fresh Windows Server 2012 install, where I'm running TeamCity.

Installing the Microsoft .NET Framework 4.5.1 Developer Pack took care of the issue (after having separately installed the MS Build Tools).

I needed to download and install the Windows 8.0 (and not 8.1) SDK to make the error disappear on my TeamCity server.

https://developer.microsoft.com/en-us/windows/downloads/windows-8-sdk

Install the .NET Runtime as well as the targeting pack for the .NET version you're targeting.

The developer pack is just these two things bundled together but as of today doesn't seem to have a 4.6 version so you'll have to install the two items separately.

Downloads can be found here: http://blogs.msdn.com/b/dotnet/p/dotnet_sdks.aspx#

For me helped only this code line:

Assembly.Load("System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a");

On our Tfs 2013 build server I had the same error, in a test project. with the main web project running on .Net 4.5.1.

I installed a nuGet package of System Runtime and added the reference from packages\System.Runtime.4.3.0\ref\net462\System.Runtime.dll

That solved it for me.

I had this problem in some solutions on VS 2015 (not MVC though), and even in the same solution on one workstation but not on another. The errors started appeared after changing .NET version to 4.6 and referencing PCL.

The solution is simple: Close the solution and delete the hidden .vs folder in the same folder as the solution.

Adding the missing references as suggested in other answers also solves the problem, but the error remains solved even after you remove the references again.

As for TeamCity, I cannot say since my configuration never had a problem. But make sure that you reset the working catalog as a part of your debugging effort.

I was also facing this problem trying to run an ASP .NET MVC project after a minor update to our codebase, even though it compiled without errors:

Compiler Error Message: CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

Our project had never run into this problem, so I was skeptical about changing configuration files before finding out the root cause. From the error logs I was able to locate this detailed compiler output which pointed out to what was really happening:

warning CS1685: The predefined type 'System.Runtime.CompilerServices.ExtensionAttribute' is defined in multiple assemblies in the global alias; using definition from 'c:\Windows\Microsoft.NET\Framework64\v4.0.30319\mscorlib.dll'

c:\Users\Admin\Software Development\source-control\Binaries\Publish\WebApp\Views\Account\Index.cshtml(35,20): error CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\meseems.webapp\68e2ea0f\8c5ee951\assembly\dl3\52ad4dac\84698469_3bb3d401\System.Collections.Immutable.DLL: (Location of symbol related to previous error)

Apparently a new package added to our project was referencing an older version of the .NET Framework, causing the "definition in multiple assemblies" issue (CS1685), which led to the razor view compiler error at runtime.

I removed the incompatible package (System.Collections.Immutable.dll) and the problem stopped occurring. However, if the package cannot be removed in your project you will need to try Baahubali's answer.

install https://www.microsoft.com/en-us/download/details.aspx?id=49978 Microsoft .NET Framework 4.6.1 Developer Pack and add this line of code in Web.config file

<compilation debug="true" targetFramework="4.5">
          <assemblies>
            <add assembly="System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
          </assemblies>
        </compilation>

I copy the file "C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.5.1\Facades\system.runtime.dll" to bin folder of production server, this solve the problem.