Source Viewer Error: cannot show this file

Either the file does not exist, or your configuration settings for the source viewer do not allow files in this directory to be viewed. To edit the configuration settings, see the web.config file at the root of the quickstart directory. Change the <sourceview> setting to point at the root directory of the quickstart. All files under this directory will be accessible to the source viewer.

<configuration>
  <system.web>
    <sourceview>
      <add key="root" value="c:\Program Files\Microsoft.Net\FrameworkSDK\Samples\Quickstart" />
    </sourceview>
  </system.web>
</configuration>