How I can fix MAC error in asp.net application?
<p>I have an ASP.NET application all things are working fine but after some minutes when I click on a button it gives me this error :</p>

<blockquote>
  <p><strong>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.  Description: An
  unhandled exception occurred during
  the execution of the current web
  request. Please review the stack trace
  for more information about the error
  and where it originated in the code.</strong></p>
  
  <p>Exception Details:
  System.Web.HttpException: 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 I can resolve this ?</p>
