Validation of viewstate MAC failed
<blockquote>
  <p><strong>Message:</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. Source: System.Web Inner
  Exception:System.Web.UI.ViewStateException:
  Invalid viewstate. Client IP:
  80.79.116.251 Port: 59340 User-Agent: Mozilla/4.0 (compatible; MSIE 7.0b;
  Windows NT 6.0) <br /><strong>ViewState:</strong>
  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...<br />
  <strong>Stack Trace:</strong> 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.login_aspx.ProcessRequest(HttpContext
  context) in
  c:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary
  ASP.NET
  Files\root\79794658\835d6695\App_Web_h5zykaqc.25.cs:line
  0 at
  System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
  at
  System.Web.HttpApplication.ExecuteStep(IExecutionStep
  step, Boolean&amp; completedSynchronously)</p>
</blockquote>

<p>I tried suggested solution from this article <a href="http://blogs.msdn.com/b/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx" rel="nofollow">http://blogs.msdn.com/b/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx</a>
inherit from the BasePage class but I'm still getting occasionally errors above.</p>

<p>I'm using master page and content page so content page inherited from BasePage class.
Maybe someone suggest other working solution?</p>
