Validation of viewstate MAC failed

Question

Possible Duplicate:
Setting ViewStateUserKey gives me a “Validation of viewstate MAC failed” error

I have applied the solutions of the posts on StackOverflow but they did not work out for my problem.

The details of the problem is:

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) [phone]
   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) [phone]
   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +59
   System.Web.UI.HiddenFieldPageStatePersister.Load() [phone]
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() [phone]
   System.Web.UI.Page.LoadAllState() +46
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) [phone]
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) [phone]
   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

I already tried to put this in the web.config:

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

Answer 1

I asked a similar question a while ago. Did you see this post? Another thing that helped me with this error was setting a machineKey. See this Microsoft Page about the problem and setting a Machine Key.