how to code a login page which verifi the user when correct it goes to the next page

private void Login()
{
SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=PRODUCT;Integrated Security=True");
if (con.State == ConnectionState.Closed)
{
con.Open();
}
if (txtUserName.Text == "" & txtPassword.Text == "")
{
lblMsg.Text = "User ID and Password is Required!";
}
DataSet ds = new DataSet();
//SqlDataAdapter da = new SqlDataAdapter();
string qry=("select UserName,UserPassword from tbl_Login where UserName='"+txtUserName.Text +"', and UserPassword='"+ txtPassword.Text+"'");
//SqlDataAdapter da = new SqlDataAdapter(qry,con);
// if (da.Fill(ds,"")
// {
// Response.Redirect("ItemAddrepeter.aspx");

// }
SqlCommand cmd = new SqlCommand(qry,con);
cmd.CommandType = CommandType.Text;
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
Session["Name"] = txtUserName.Text.ToString();
Session["pass"] = txtPassword.Text.ToString();
Response.Redirect("ItemAddrepeter.aspx");
}

con.Close();
}



protected void btnLogIn_Click(object sender, EventArgs e)
{
try
{
Login();
}
catch (Exception ex)
{
lblMsg.Text = ex.Message;
}
}
this is my code but this give error