Hi all,
recently, taking a look at the log i find some exceptions like the following one. Do you have any suggestion about this problem?

AssemblyVersion: 04.04.01
PortalID: 0
PortalName: mysite.com
UserID: -1
UserName:
ActiveTabID: 54
ActiveTabName: Blogs
RawURL: /DesktopModules/Blog/Blogs/tabid/54/EntryID/4/Default.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.mysite.com/Blogs/tabid/54/EntryID/4/DesktopModules/Blog/ImageChallenge.captcha.aspx?captcha=1C6F8734876963E026BE2E889AD487E40D3A7EDFB9A4ACA8C5642577BB9E922F41A163F92CD97A0A02F6A0A89A34E33306EE6D5D6CD8B4737A9C945183D16E049CBF96D06F02F51A653EE1F24B39D3F9480C4083EC5706A556D4AD3C6875A60CB30685B9AB4CDFE1CB762E8DCB4B0C558CD57A4C3ADB72F0
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 077d6c5a-99ce-429a-8e42-77651afcbb73
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: System.Web.Configuration.MachineKeySection.GetDecodedData
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: 66.65.47.104 Port: 42152 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0 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.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: WEBS147

Just upgraded to DNN 4.8.2 and now I'm getting this message also.

Sorry for being so ignorant, but how do we do this??  Can someone confirm this solution works??

Thanx!