Validation of viewstate MAC failed

View Log Entry Details (back to system log)
  Log type:  Unknown
  Severity:  11
  
Message:  Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.
  
Exception:  System.Web.HttpException (0x80004005): Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: 72.167.191.6 Port: 50437 Referer: Path: /conditionsinfo.aspx User-Agent: Mozilla/5.0 (compatible; MSIE 7.0; MSIE 6.0; Site Scanner; +http://www.websiteprotection.com) Firefox/2.0.0.3 ViewState: VzLxjwSZcbI0fwqXc4Xd05hM bB9SbtEFOuTseyHMC68QVz/Iq2AmlUNa /ekxYGSE10cXJL0Rex/2lijAUwuPn6QfEaGaBjt7Hz6a8EEdxY2jBSmEGOdLFLwfQLUiK7BfIB4 eDow4qHQL5WYiLYPv dggwAn7x8QfzpyOSc6Btz7mTce 5Ad/HGH64jEUO8Dyb f5RhfKm6bIDDkmXdXDEvs8k62IPRE A5vyUJmq e6bOO5LPNtCiTv df13ZVslsRmU9CrfwRczRM 8WvngF92PMeXZaCM7nvbaGef1MYzBt1ro8iSMahq/CugomGR1HwrndWvpXHrLq9fFnRY9PE7kXFlZooOSj6r72Lfr ma0FOKMSddvewum6 6sqJhBmewl9P43MNATiW0qtE bDT6 W7cxZ4Lh4Y4f tQNtzeoZie99nWnuB6 m4FyLHxiRUgr/6joYZOnjvkEIfJfqpQvv1E3dOotVk6ZXvekxxA760jbnIDTTjx43Tb18NDSi7mUGQvgDD/RXFIYDfAcriD JocFuYAbAycIlrK4qL5QEfCCLeRr4QUiaxo/0QXP5 LQG3gzBBemjvsm8b3HtblSYwxnuSNJSbbmCno aDkNXkQ H7nvvRfs/A8zqIsnjr9DNk9IyDkbEurIeDxmuCyU3nxaiOa6Q0H/IToKf9h1X9Phk93OVouyuJ27v2qXXnitumERm3K5IDjxGx7LXR0NjqiqszJmyhufxuU eiFPMjToolN202rZ7rBKR3M/yRpqBveGqYTvZlZndXov/Xfbn/AKmpV... ---> System.Security.Cryptography.CryptographicException: Length of the data to decrypt is invalid. at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount) at System.Security.Cryptography.CryptoStream.FlushFinalBlock() at System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean fEncrypt, Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Boolean useValidationSymAlgo, Boolean useLegacyMode, IVType ivType) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) --- End of inner exception stack trace --- 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.conditionsinfo_aspx.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
  IP address:  72.167.191.6
  Customer:  
  Page URL:  http://lebanese-market.com/conditionsinfo.aspx
  Referrer:  
  Created on:  4/7/2011 1:28:27 AM

Please look at the following topic https://www.nopcommerce.com/boards/t/2857/validation-of-viewstate-mac-failed.aspx