Resolving view state message authentication code (MAC) errors

Server Error in '/' Application.

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: ... Line: 0

Stack Trace:

[ViewStateException: Invalid viewstate.

Client IP: ::1

Port: 40653

Referer: http://localhost:40643/MyPage.aspx

Path: /MyPage.aspx

User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident/6.0)

ViewState: ...]

[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.

See http://go.microsoft.com/fwlink/?LinkID=314055 for more information.]

System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +190

System.Web.UI.ViewStateException.ThrowMacValidationError(Exception inner, String persistedState) +46

System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) +861

System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter2.Deserialize(String serializedState, Purpose purpose) +51

System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) +67

System.Web.UI.HiddenFieldPageStatePersister.Load() +444

System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +368

System.Web.UI.Page.LoadAllState() +109

System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +7959

System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +429

System.Web.UI.Page.ProcessRequest() +125

System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +48

System.Web.UI.Page.ProcessRequest(HttpContext context) +234

ASP.mypage_aspx.ProcessRequest(HttpContext context) in ...:0

System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +1300

System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +140

Resolve this issue you can add a <machineKey> element, in the Web.config file. The <machineKey> element is only valid in the Web.config file at the root of your application and is not valid at the subfolder level.

<configuration>

  <system.web>

    <machineKey ... />  (add below machineKey in system.web section)

  </system.web>

</configuration>

<machineKey

validationKey="20A1D0BF6A9C13FC54FAFAE5534D586F78A50005223F08C0C8AD0704CCF27C29E6F41C30FA03D9E418F7EBB38BFDAC698545C39200C39A622BE22EBC6C10BEE8"

decryptionKey="CD0F6DC238FD884B009B3C5E3163726F58C4D51FE82908E9F1504BF50D95075D"

validation="SHA1" decryption="AES"/>