title: File (or assembly) can't be found after changing project's .NET target-framework from 4.0 to 3.5
body: <p>I want to change my C# project, which is based on the .NET 4.0 to 3.5.
  So I changed the project's target-framework to 3.5.</p>
  
  <p>After re-opening and trying to compile the project I get the error:</p>
  
  <blockquote>
    <p>The file or assembly "System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" or one of its dependencies couldn't be found. The system can't find the file.
    oder eine Abhängigkeit davon wurde nicht gefunden. Das System kann die angegebene Datei nicht finden.</p>
  </blockquote>
  
  <p>This happens in the file Resource.resx, which looks like that:</p>
  
  <pre><code>&lt;assembly alias="System.Windows.Forms" name="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /&gt;
      &lt;data name="traktor_connected" type="System.Resources.ResXFileRef, System.Windows.Forms"&gt;
          &lt;value&gt;..\Resources\traktor_connected.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a&lt;/value&gt;
      &lt;/data&gt;
      &lt;data name="traktor_not_connected" type="System.Resources.ResXFileRef, System.Windows.Forms"&gt;
          &lt;value&gt;..\Resources\traktor-not-connected.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a&lt;/value&gt;
      &lt;/data&gt;
  </code></pre>