The type or namespace name 'Exchange' does not exist in the namespace
<p>When I run my ASP.net app I get this error:</p>

<pre><code>Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 
</code></pre>

<p>Compiler Error Message: CS0234: The type or namespace name 'Exchange' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)</p>

<p>Source Error:</p>

<pre><code>   Line 06:  using System.Web.UI.WebControls;
   Line 07:  using System.Data.OleDb;
   Line 08:  using Microsoft.Exchange.WebServices.Data; // error
   Line 09:  using System.Net;
   Line 10:  using System.Data.SqlClient;
</code></pre>
