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http://hosting.india.to/clients/knowledgebase/175/Validation-of-viewstate-MAC-failed-If-this-application-is-hosted-by-a-Web-Farm-or-cluster-ensure-that-andltmachineKeyandgt-configuration-specifies-the-same-validationKey-and-validation-algorithm-AutoGenerate-cannot-be-used-in-a-cluster.html