Complete Error Message
Before you start your troubleshooting, make sure that the State Service service application is running. How you will check this?
Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration.
