Possible Duplicate:
definição de ViewStateUserKey fornece um erro de "Validação do viewstate MAC falhou"

Apliquei as soluções das postagens no StackOverflow, mas elas não funcionaram no meu problem

Os detalhes do problema são:

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.

[HttpException (0x80004005): Unable to validate data.]
   System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) +10986325
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +295

[ViewStateException: Invalid viewstate. 
    Client IP: 131.155.68.60
    Port: 53999
    User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.204 Safari/534.16
    ViewState: /wEPDwULLTIxNDQxNzQ5ODlkZDYHBedPRvEzZrTTrJvp9yAr5yfa
    Referer: http://rms.rextron.eu/login.aspx?ReturnUrl=%2fdefault.aspx
    Path: /login.aspx]

[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) +148
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +10959605
   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +59
   System.Web.UI.HiddenFieldPageStatePersister.Load() +10959704
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +11043464
   System.Web.UI.Page.LoadAllState() +46
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +11038983
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +11038522
   System.Web.UI.Page.ProcessRequest() +91
   System.Web.UI.Page.ProcessRequest(HttpContext context) +240
   ASP.login_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework64\v2.0.50727\Temporary ASP.NET Files\root\9ec5a6be\294c12de\App_Web_ptjxac-a.1.cs:0
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +599
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +171

Já tentei colocar isso no web.config:

<pages validateRequest="false" enableEventValidation="false" viewStateEncryptionMode ="Never">