Suddenly getting this error message on login process

Question

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that 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.

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 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.

Source Error: 

 

The source code that generated this unhandled exception can only be shown when compiled in debug mode. To enable this, please follow one of the below steps, then request the URL:

1. Add a "Debug=true" directive at the top of the file that generated the error. Example:

<%@ Page Language="C#" Debug="true" %>

or:

2) Add the following section to the configuration file of your application:

<configuration>

<system.web>

<compilation debug="true"/>

</system.web>

</configuration>

Note that this second technique will cause all files within a given application to be compiled in debug mode. The first technique will cause only that particular file to be compiled in debug mode.

Important: Running applications in debug mode does incur a memory/performance overhead. You should make sure that an application has debugging disabled before deploying into production scenario.

 

Stack Trace: 

[ViewStateException: Invalid viewstate. Client IP: 127.0.0.1 Port: Referer: http://localhost:52635/Login.aspx Path: /CDFQuarterlyReportPage.aspx User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36 ViewState: /wEPDwUKMTg2NTY2OTU4Ng9kFgICAw9kFgICFQ8PZBYCHgdvbmNsaWNrBYIDaWYgKHR5cGVvZihQYWdlX0NsaWVudFZhbGlkYXRlKSA9PSAnZnVuY3Rpb24nKXsJdmFyIG9sZFBhZ2VfSXNWYWxpZCA9IFBhZ2VfSXNWYWxpZDsJdmFyIG9sZFBhZ2VfQmxvY2tTdWJtaXQgPSBQYWdlX0Jsb2NrU3VibWl0OwlpZiAoUGFnZV9DbGllbnRWYWxpZGF0ZSgnJykgPT0gZmFsc2UpCXsJCVBhZ2VfSXNWYWxpZCA9IG9sZFBhZ2VfSXNWYWxpZDsJCVBhZ2VfQmxvY2tTdWJtaXQgPSBvbGRQYWdlX0Jsb2NrU3VibWl0OwkJcmV0dXJuIGZhbHNlOwl9fXRoaXMuY2xhc3NOYW1lID0gJ0J1dHRvblBsZWFzZVdhaXQnO3RoaXMudmFsdWUgPSAnUGxlYXNlIHdhaXQuLi4nO3RoaXMuZGlzYWJsZWQgPSB0cnVlO19fZG9Qb3N0QmFjaygnYnRuTG9naW4nLCcnKTtyZXR1cm4gdHJ1ZTtkGAEFHl9fQ29udHJvbHNSZXF1aXJlUG9zdEJhY2tLZXlfXxYBBQhyZW1lbWJlcpIsWU6rkKU3FaXYs1Ua61MlHlxTjXZRTWYJBZobpHa2] [HttpException (0x80004005): Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that 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) +116 System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) +432 System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter2.Deserialize(String serializedState, Purpose purpose) +8 System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) +40 System.Web.UI.HiddenFieldPageStatePersister.Load() +248 System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +272 System.Web.UI.Page.LoadAllState() +36 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6704 System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +245 System.Web.UI.Page.ProcessRequest() +72 System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +21 System.Web.UI.Page.ProcessRequest(HttpContext context) +58 ASP.cdfquarterlyreportpage_aspx.ProcessRequest(HttpContext context) +37 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +341 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69  

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Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34248