Validation of viewstate MAC failed
<p>Running the ASP.NET webforms run the application works fine. When the application is idle for 4 to 5 minutes, it is giving this error:</p>

<blockquote>
  <p>Validation of viewstate MAC failed. If
  this application is hosted by a Web
  Farm or cluster, ensure that
   configuration specifies
  the same validationKey and validation
  algorithm. AutoGenerate cannot be used
  in a cluster.</p>
</blockquote>

<p>How can this be solved?</p>
