Invalid Attempt To Read When No Data Is Present?

i got the error when try to select values from database "Invalid attempt to read when no data is present."

i used this code

SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["ab"].ToString());
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select userid,password from pro_table where userid='"+TextBox1.Text+"'";
SqlDataReader dr;
con.Open();
dr = cmd.ExecuteReader();
dr.Read();
if (dr[1].ToString() == TextBox1.Text && dr[0].ToString() == TextBox2.Text)
{
Response.Redirect("welcome.aspx");
}
else
{
Label4.Text = "User id or password is invalid";
}
con.Close();