title: SortedList<TKey, TValue> not defined in Systems.Collections.Generic using .NET 4.0
body: <p>I downloaded a library that uses the generic version of <code>SortedList</code>, but when I try to compile it the following error pops up:</p>
  
  <p><code>The type or namespace name 'SortedList' does not exist in the namespace 'System.Collections.Generic' (are you missing an assembly reference?)</code></p>
  
  <p>I tried to fix it using the full namespace, <code>System.Collections.Generic.SortedList&lt;string, string&gt;</code> but still no luck, the same error.</p>
  
  <p>I looked up in MSDN and it says that SortedList is supported on .NET 4.0 (the version I am currently using).</p>
  
  <p>Also, my projects references the mentioned namespaces.</p>
  
  <p>This is the code (the error gets repeated more than once, for every reference to SortedList):</p>
  
  <pre><code>public class Map
  {
      public SortedList&lt;string, Tileset&gt; Tilesets = new SortedList&lt;string, Tileset&gt;();
      public SortedList&lt;string, Layer&gt; Layers = new SortedList&lt;string, Layer&gt;();
      public SortedList&lt;string, ObjectGroup&gt; ObjectGroups = new SortedList&lt;string, ObjectGroup&gt;();
      public SortedList&lt;string, string&gt; Properties = new SortedList&lt;string, string&gt;();
      public int Width, Height;
      public int TileWidth, TileHeight;
  }
  </code></pre>