cannot find table 0 in login form

hey all
 
i have 1 login form for 2 users one is admin and second is simple user
 
when i login from theri password then its fine and working but when ienter worng password it gives me error CANNOT FIND TABLE 0
 
CODE
 

public int Loginuser1(string UserName, string Password)
        {
            // return the values if Admin then 1 else 2 for User
           int a = Convert.ToInt32( db.ExecuteDataSet("splogin3", new object[] { UserName, Password }).Tables[0].Rows[0][0].ToString());
           return a;
        }

AND login button code is

protected void Button1_Click(object sender, EventArgs e)
        {
            if (cd.Loginuser1(UserName.Text, Password.Text)==1)
            {
                Session["UserID2"] = cd.Loginuser1(UserName.Text, Password.Text);
                Session["Login4"] = UserName.Text;
                Session["Login5"] = Password.Text;
                Lgin.Text = ("Login Successfully");
                Response.Redirect("DocUpload.aspx");

 
                Lgin.Text = ("Incorrect Passsword");
            }
 
            else if (cd.Loginuser1(UserName.Text, Password.Text)==2)
            {
                Session["UserID"] = cd.Loginuser1(UserName.Text, Password.Text);
                Session["Login2"] = UserName.Text;
                Session["Login3"] = Password.Text;
                Lgin.Text = ("Login Successfully");
                Response.Redirect("InfoDoc.aspx");
 
                Lgin.Text = ("Incorrect Passsword");
            }
        }