title: Viewstate exception
body: <p>In our website (ASP.NET Forms, Sitecore 6.6), in the log files I find so many viewstate exceptions. But there is no obvious issues reported by the users.</p>
  
  <p>Here is the exception, by referring to the log files I found that this issue mainly occurs in a particular page which has a viewstate like 20KB. Please help to sort out this issue. </p>
  
  <pre><code>5676 00:30:43 ERROR Application error. 
  Exception: System.Web.HttpException 
  Message: The client disconnected. 
  Source: System.Web 
  at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) 
  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(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) 
  at System.Web.UI.Page.ProcessRequest() 
  at System.Web.UI.Page.ProcessRequest(HttpContext context) 
  at System.Web.UI.Page.ProcessRequest(HttpContext context) 
  at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 
  at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 
  at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously) 
  
  Nested Exception 
  
  Exception: System.Web.UI.ViewStateException 
  Message: Invalid viewstate. 
  Client IP: xxx.xxx.xxx.249 
  Port: 53377 
  Referer: &lt;URL&gt;
  Path: /&lt;PATH&gt;
  User-Agent: Mozilla/5.0 (iPad; CPU OS 6_1_3 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B329 Safari/8536.25 
  ViewState: cT4jo/ieR1NMvyqfwH6MToZmW6E/oKO64RcFXyllzcXB84wiWN/j3WeRyXxUZWCnr9c6staUp76B0Zr7/IqYgWWS3qfiMu9xzpU61bB+TAjDz0IbVwSt0rvZoFh7M/tQGQWyRha4ieCH7B5wKu3hXexRTIWwvP0JLbNmnQyFnOdqTnJZXBYQtaTyzMva3Fy7Q9YNstymtd1XrO1WHvUsBS6CwyV8eUYZs3LWRvczf3Ixz2XRg2Y4fY4kpuXl+QJLkbhgnALcFeGe9ur1l8Gyq6EdhqRb0BOlK4ozKaq4hpUT6HWes9YP2DjCJCpa2wP47hqZ5DaAXrcN+R6UPOqYIl6TSIjNUCv35NPPozaFjItLGmZi6ee+PfxOSz4ejxgBJzV3KNf2/1Mr5GNI7uZWgw998CI0mtxtpuWjp5kZCAfKzSCX//Vv7030VBLAE4Gj1RYIek1WNuwDreglFE5Pt8uKMDOsJstt8tXGqyCVcxqQAnRyN51e3uuqbDvDL2yVXA6yv6QyaCD/XmIHcgz//HItyqlhEziyOx7MxwKzpMyLu/6g2poqKMoNWtnQwxw9JTVwijEf45Lai+BOmgMNITgyrmLDp7ioHgHFK0VSmrSxN2W+CBRyyXWfn3QAy8UQYpq1TdHEUnGbc3XTTfBYW/gj+mFGaEpM24hUi/gJBxU2r+/wG2XxHfsxgrq6kG5cM8Hzf4GHuSC4...
  
  Nested Exception 
  
  Exception: System.FormatException 
  Message: Invalid length for a Base-64 char array or string. 
  Source: mscorlib 
  at System.Convert.FromBase64_Decode(Char* startInputPtr, Int32 inputLength, Byte* startDestPtr, Int32 destLength) 
  at System.Convert.FromBase64CharPtr(Char* inputPtr, Int32 inputLength) 
  at System.Convert.FromBase64String(String s) 
  at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) 
  at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) 
  at System.Web.UI.HiddenFieldPageStatePersister.Load() 
  </code></pre>