title: Validation of viewstate MAC failed
body: <p>i am getting this exception help me how to solve this problem.</p>
  
  <pre><code>Error Time      : 20091104 151412
  Error Message   : 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.
  Source          : System.Web
  StackTrace      : at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError)
     at System.Web.UI.ViewStateException.ThrowMacValidationError(Exception inner, String persistedState)
     at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)
     at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState)
     at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState)
     at System.Web.UI.HiddenFieldPageStatePersister.Load()
     at System.Web.UI.Page.LoadPageStateFromPersistenceMedium()
     at System.Web.UI.Page.LoadAllState()
     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
     at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
     at System.Web.UI.Page.ProcessRequest()
     at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
     at System.Web.UI.Page.ProcessRequest(HttpContext context)
     at ASP.bla_bls_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\87932190\f6393965\App_Web_slwxkxn3.2.cs:line 0
     at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously)
  Target Site     : Void ThrowError(System.Exception, System.String, System.String, Boolean)
  Inner Exception : System.Web.UI.ViewStateException: Invalid viewstate. 
      Client IP: 172.16.153.71
      Port: 1466
      User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 2.0.50727)
      ViewState: 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... ---&gt; System.Web.HttpException: Unable to validate data.
     at System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32&amp; dataLength)
     at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)
     --- End of inner exception stack trace ---
  </code></pre>