I am building website in local and  sometimes I catch  a following error when load website. I don't know this error. Could you help me? 

DotNetNuke.Services.Exceptions.PageLoadException: 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. ---> 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. ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: 127.0.0.1 Port: 1325 User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729) ViewState: 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... ---> System.Web.HttpException: Unable to validate data. at System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) --- End of inner exception stack trace --- --- End of inner exception stack trace --- at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) at System.Web.UI.ViewStateException.ThrowMacValidationError(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 ---