title: .NET/Silverlight Missing DLL
body: <p>I am inheriting a Silverlight project from a developer who just upped-and-quit and left behind no instructions or documentation (whatsoever). Scrambling to pick up the pieces and get my sandbox working.</p>
  
  <p>Company gave me a license for VS 2010 Developer, which I have installed.  I open the project's SOLUTION file and try to clean -> build it, but getting a compiler error. It's missing the <code>System.Windows.Interactivity.dll</code> file. I have already installed Silverlight SDK and Expression Blend, which are the two places previous SO questions (<em>similar</em> to this, but not identical!) recommended looking.</p>
  
  <p>Although I do see it inside Expression Blend's installation, when I try to add it as a reference to the Silverlight project, I get the following error:</p>
  
  <blockquote>
    <p>You can't add a reference to System.Windows.Interactivity.dll as it was not built against the Silverlight runtime. Silverlight projects will only work with Silverlight assemblies.</p>
  </blockquote>
  
  <p>What are my options here?!? Thanks in advance.</p>