Hello,
Please help. After upgrading to DNN ver. 9.1.1 I started getting this Page Load Exception:

InnerMessage: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.

InnerStackTrace:
at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidati ) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) 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)
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I have searched the Internet but could find the remedy.

Thanks,
Vladimir

Thank you, Sebastian.
Still the question remains. At what point (i.e. when and why) the page load exception is generated? Should I check the site settings and do something or is it a minor error that I can ignore?

Thank you Sebastian. Now it's clear. The error was thrown while I was updating the contents of my site.

Vladimir