Runtime: System.IO.FileNotFoundException: Could not load file or assembly 'System.Net.Http, Version=4.1.1.0

[shravan2x]

I recently created a .NET Core 2.0 library that multitargeted net46. It included this in the .csproj file:

  <ItemGroup Condition="'$(TargetFramework)'=='net46'">
    <Reference Include="System.Net.Http" />
  </ItemGroup>

  <ItemGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
    <PackageReference Include="System.Net.Http" Version="4.3.3" />
    <PackageReference Include="System.Net.Primitives" Version="4.3.0" />
    <PackageReference Include="System.Net.Requests" Version="4.3.0" />
    <PackageReference Include="System.Net.Sockets" Version="4.3.0" />
  </ItemGroup>

I referenced this library is a .NET Framework 4.7 console app and get this exception:

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.Net.Http, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified. ---> System.IO.FileNotFoundException: Could not load file or assembly 'System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

I didn't see any warnings in the error list, but I decided to check the build log and found a conflict.

This is what I see in the detailed build log:

1>  There was a conflict between "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "System.Net.Http, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".
1>      "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" was chosen because it was primary and "System.Net.Http, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" was not.
1>      References which depend on "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" [C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7\System.Net.Http.dll].
1>          C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7\System.Net.Http.dll
1>            Project file item includes which caused reference "C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7\System.Net.Http.dll".
1>              System.Net.Http

My App.config includes a redirect which should have been used

<dependentAssembly>
        <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.1.1.0" newVersion="4.1.1.0" />
      </dependentAssembly>

What I don't fully understand in why System.Net.Http includes a reference to itself. Is this corruption of some sort or am I missing something?

[karelz]

System.Net.Http.dll 4.1.1.0 shipped in nuget package System.Net.Http 4.3.0. It caused a problem on .NET Framework - see dotnet/runtime#18280 for details.
We shipped updated package System.Net.Http 4.3.1 which passes through to the underlying platform on .NET Framework (with assembly version 4.0.0.0).
I assume something in your app is referencing older nuget package with higher assembly version. You need a binding redirect like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            <dependentAssembly>
                <assemblyIdentity name="System.Net.Http" culture="neutral" publicKeyToken="b03f5f7f11d50a3a" />
                <bindingRedirect oldVersion="0.0.0.0-4.1.1.0" newVersion="4.0.0.0" />
            </dependentAssembly>
        </assemblyBinding>
    </runtime>
</configuration>

[shravan2x]

@karelz The issue is that I do not use System.Net.Http 4.3.0 anywhere. My multi target for netstandard2.0 uses version 4.3.3 and the reference for net46 directly uses an assembly reference <Reference Include="System.Net.Http" />.

Also, the project that uses the library already has the binding redirect you mentioned.

      <dependentAssembly>
        <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.1.1.0" newVersion="4.1.1.0" />
      </dependentAssembly>

EDIT: Nevermind I didn't notice the newVersion in your post was different than mine. Your fix seems to work for me.

I vaguely remember encountering this issue in the past; it might help future users to maintain a wiki page for this issue with enough keywords that it shows up in a google search.

Thanks for the help!

[fernandozamoraj]

In my case the team was using Visual Studio 2019. I was using VS 2015 because that is what the sln would default to. Once I opened in in VS 2019 it worked. I guess that's because of the references in one applicaiton vs. the other. And actually in my case it was the System.Net.Sockets file.