title: Could not load file or assembly 'Microsoft.Scripting.ExtensionAttribute...' after .NET 2 to 4 migration
body: <p>I am in the process of converting quite a few .NET 2 ASP.NET web apps to .NET 4. One of the problems I've encountered during this process is the following error message - </p>
  
  <pre><code>Could not load file or assembly 'Microsoft.Scripting.ExtensionAttribute, Version=0.9.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. 
  </code></pre>
  
  <p>The error also highlights the line of code which is the culprit, which for me, in my ScriptManager - </p>
  
  <pre><code>&lt;asp:ScriptManager ID="ScriptManager1" EnablePartialRendering="true" runat="server"&gt;
  &lt;/asp:ScriptManager&gt;
  </code></pre>
  
  <p>The strange thing I've noticed is that this error simply disappears as soon as the page is refreshed, but will reappear if I recycle the application pool (and I'm guessing if I publish the web app again).</p>
  
  <p>Most of my research has lead to dead ends, which mostly point the finger of blame to Umbraco (which is not being used at all) and IronPython (which I admit, is used in another project in the same solution, but not the project in question).</p>
  
  <p>I can't really have these web apps breaking every time I make a change to the site, does anyone have any ideas?</p>