By default, in requests from the Windows Client Web Designer to the server there is no support to use HttpContext.Session because this has a bad impact on the application performance. Set this property to True to be able to use HttpContext.Session in server code that is called from the Windows Client Web Designer (e.g. in your repository class).

public static bool EnableSessionState {get; set;}

public:
static property bool EnableSessionState {
   bool get();
   void set (    bool value);
}

'Declaration
 
Public Shared Property EnableSessionState As Boolean