I had a simple Portable Class Library project which used Microsoft HTTP Client Libraries (System.Net.Http.HttpClient). The problem: The Visual Studio wouldn’t compile it:

The type or namespace name ''Http'' does not exist in the namespace ''System.Net'' (are you missing an assembly reference?)

The PCL project targeted the following frameworks:

  • Windows Phone 8
  • Silverlight 5
  • .NET 4.5
  • Windows Store apps

I was using the stable 2.1.10 release of the HttpClient library. Resharper didn’t find anything wrong with the code but still it wouldn’t compile. So I created an another PCL project, added the same HttpClient NuGet package and the same code. And it compiled without a problem.

So I had two identical projects with identical references and with identical code. But only one of them compiled.

I decided to diff the project files and this helped me to notice that the non-compiling project had an app.config –file:


And the configuration contained bindingRedirects:

<?xml version="1.0" encoding="utf-8"?>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <assemblyIdentity name="System.Threading.Tasks" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="" newVersion="" />

When I created the non-compiling PCL project, I set some of the target frameworks wrong. Because of this, it seems, the HttpClient Nuget-package added the configuration. And this broke the compilation after I had fixed the target frameworks.

The solution was simple: I just had to remove the runtime-element from the configuration.