In VS 2010, if you are accessing the Session state in the OnInit(…) method of your page, similar to the following code snippet: then you will encounter an “Error Creating Control” for ASP.NET controls when viewing the Design view of the page. For example, if you have an ASP.NET button control on the page, the designer will display the error: “ Error Creating Control – Button1 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.”. Screen shot of the error: However…(read more)