title: Asp.net Validation of viewstate MAC failed
body: <p>I am receiving the following error at certain times on asp.net website.</p>
  
  <pre><code> Sys.WebForms.PageRequestManagerServerErrorException: 
   Validation of viewstate MAC failed. 
   If this application is hosted by a Web Farm or cluster,
   ensure that &lt;machineKey&gt; configuration specifies the 
   same validationKey and validation algorithm. 
   AutoGenerate cannot be used in a cluster.
  </code></pre>
  
  <p>When page refresh goes,no problem.How can I solve this problem?</p>