Hi,
We have been getting errors on DotNetNuke production site when trying to access the Site Settings page and add/edit any articles using one of the modules (DNNArticle module) that are installed on the website. The error on the page is “A critical error has occurred. Object reference not set to an instance of an object.”. Please see below for the event log:
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: 178.137.163.48 Port: 62863 Referer: http://www.acceleratingitsuccess.com/Articles/tabid/1450/ArticleId/8038/Bridging-the-Gap-Between-the-CIO-and-the-Board.aspx/uid/3367 Path: /Default.aspx User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.5 (KHTML, like Gecko) YaBrowser/1.1.1084.5409 Chrome/19.1.1084.5409 Safari/536.5 ViewState: +7kZR/24p6nXjq5+gHrCEf6G4K6Rm7abQUM4p3HirfKnU9dHnXJIjD9zJmOGipVLnVgf3I9WYN3WaHqDmM8BWwfC06zlyewgpz5aKRq/LjDBdYmjAXRG78opKnzl780wvfLLERIYvmCIIsUjbH8eg70x4JZKuRSe5GjAWsMXgjT0VuQMsKl17YEfJ30Oboa7iUz7z2nhBUJw828HRT+81N0eqAHucgeXmwiDiE6tz7kALfxJAPfidhKIu2yH0EvtRxyaV++e4D6fmJ6Rcyp1gO4KDVMYtXN86dD/6Ygv/vpo5J80Fhonm6WUBz2l8MwQ1zrYDEvXaY2kVK1R4bjWETk0lk0zd5g9TnYIdFM/xHdlnX1L8Ki5OyTikDdScUiq4V70tDWENJgsaOWKCOXf4OwPbPnjCpC9TnyanTSKYvxoLr0iRzaqK9txmmU0NRZ6dYtIq6uoJxQKqKE91TblgbA14f1jOptcvnaLYuNDGbKsAe1cHFTQeWVHTvsebKNfcEiL7xf88qQWaAYCUwzsXuNk9hR7Bc4LoVAUFn4qOOmITdqzeNM89u/e9cgeDzb37NhEy6Sjh4Fcda1x+v4n2dwrJyL59Pe2KXYbTYP7DGwuAMZe1QBz9e5m5KsDkA7/yfR8XWDunnjyRPlku19... --- 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 ---
DotNetNuke version: 6.2.3
.Net Framework: 4.0

Thank you.

Best regards,
Sushan