title: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly but it's not mscorlib
body: <p>I am getting this exception message when I try to run my Visual Studio 2013 Web Application:</p>
  
  <pre><code>"Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'Bridge, Version=1.0.1.30841, Culture=neutral, PublicKeyToken=null'."
  </code></pre>
  
  <p>I found lots of pages about this attribute moving between 4.0 and 4.5, but I am running .NET 4.6.1, and compiling the assemblies to 4.6.1.  Also, this error is not about mscorlib, it is about an assembly I am building myself, named Bridge.  I don't understand why there is a reference to System.Runtime.CompilerServices.ExtensionAttribute in my assembly, and I am not sure what I should do to make it stop.  Advice?</p>