system.net.htt.dll

  1. Delete referenced by GAC dll .csproj - (<Reference Include="System.Net.Http" />)
  2. Check assembly binding - must be the same in all projects
<dependentAssembly>
  <assemblyIdentity name="System.Net.Http" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
  <bindingRedirect oldVersion="0.0.0.0-4.2.0.0" newVersion="4.1.1.2" />
</dependentAssembly>