Hello all,
Recently, I have been receiving a number of "Validation of viewstate MAC failed" errors in my DNN event viewer. It was suggested to me that a possible fix may be to change the "form authentication timeout" in my web.config file

"I have done some research on this issue and have come across a solution which seems to indicate a session timeout on your web server.Try to set form authentication timeout less than your session timeout in web config e.g  DNN does not use sessions, but default session timeout is 20 minutes if they are used."

Does this sound like a correct course of action? I did some googling on the topic, and I can't find any mention of where in the web.config file this value resides. 

Thanks - Alex

Full Error Message from DNN event viewer:

AssemblyVersion: 6.2.4

PortalID: 0

PortalName: YandasMusic.com - Online Music Web Store

UserID: -1

UserName:

ActiveTabID: 55

ActiveTabName: Start

RawURL: /Start/tabid/55/ctl/Login/Default.aspx?returnurl=%2f

AbsoluteURL: /Default.aspx

AbsoluteURLReferrer: http://www.yandasmusic.com/Start/tabid/55/ctl/Login/Default.aspx?returnurl=%2f

UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.1634 Safari/535.19 YE

DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider

ExceptionGUID: d9db94fd-3eb5-4727-9582-cdaff5dd8673

InnerException: 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.

FileName:

FileLineNumber: 0

FileColumnNumber: 0

Method:

StackTrace:

Message: DotNetNuke.Services.Exceptions.PageLoadException: 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.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. ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: 91.236.74.120 Port: 60417 Referer: http://www.yandasmusic.com/Start/tabid/55/ctl/Login/Default.aspx?returnurl=%2f Path: /Default.aspx User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.1634 Safari/535.19 YE ViewState: 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... --- End of inner exception stack trace --- at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidati ) at System.Web.UI.ViewStateException.ThrowMacValidati (Exception inner, String persistedState) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) at System.Web.UI.HiddenFieldPageStatePersister.Load() at System.Web.UI.Page.LoadPageStateFromPersistenceMedium() at System.Web.UI.Page.LoadAllState() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

Source:

Server Name: CLOUD278