Nilkamal

Session["userName"] = ds4Login.Tables[0].Rows[0]["userName"].ToString();
Session["userType"] = ds4Login.Tables[0].Rows[0]["userType"].ToString();

You have set Session["userName"] and Session["userType"] but not Session["userId"]..

set it before accessing and write some defensive code like:

int userId;

if(Session["userId"] != null)

{

userId=(int)session["userId"];

}