Server Error in '/' Application.Validation of viewstate MAC failed.

Server Error in '/' Application.

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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.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: 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.

Source Error:

[No relevant source lines]

Source File: c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\e136d9bf\f995111b\App_Web_qhspoarz.4.cs    Line: 0

Stack Trace:

[HttpException (0x80004005): Unable to validate data.]    System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) +353    System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +199 [ViewStateException: Invalid viewstate.         Client IP: 127.0.0.1         Port:         User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13         ViewState: 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...] [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.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +119    System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +236    System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) +5    System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +37    System.Web.UI.HiddenFieldPageStatePersister.Load() +222    System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +80    System.Web.UI.Page.LoadAllState() +35    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +7992    System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +158    System.Web.UI.Page.ProcessRequest() +85    System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +20    System.Web.UI.Page.ProcessRequest(HttpContext context) +110    ASP.registration_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\e136d9bf\f995111b\App_Web_qhspoarz.4.cs:0    System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +317    System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +65

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Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.42

ANSWER: using the following in the web.config of each website: enableViewStateMac="false" viewStateEncryptionMode="Never" enableEventValidation="false"