title: Viewstate exceptions
body: <p>I get the following exceptions every couple of days:</p>
  
  <pre><code>System.Web.HttpException (0x80004005): 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. ---&gt; System.Web.UI.ViewStateException: Invalid viewstate. 
  </code></pre>
  
  <p>The thing is that I have a machine key set, and I also use only a single server (ie no cluster). So why is this exception happening? The only thing I can think of is that I keep reseting the IIS server, but I can't quite work out why that's a problem. Do you guys see this exception on a regular basis?</p>
  
  <p>For reference, the following exists under my 'system.web':</p>
  
  <pre><code>&lt;machineKey validationKey="Blah1" decryptionKey="Blah2" validation="SHA1" decryption="AES" /&gt;
  </code></pre>