ASP.NET C# MySql

Question

Hi,

  i'm new to this field.Now i'm trying to create login form with MySql as DB.I've following error.

Can anyone help me?

On SubmitButton_Click onclick event:

string constr = "server=localhost;user name=root;password=pwd;database=contacts";

            MySqlConnection con = new MySqlConnection(constr);            

            query = "SELECT Count(*) FROM contacts WHERE username='" + nametxt.Text + "' AND password='" + pwdtxt.Text + "'";

            MySqlCommand com = new MySqlCommand(query, con);

            con.Open();

            string result = string.Empty;

            int aa = Convert.ToInt32(com.ExecuteScalar().ToString());

            con.Close();            

            if(aa==0)

            {

                lblerr.Text = "Invalid username or password";                

            }

            else

            {

                Response.Redirect("detailadd.aspx");                

            }

error:

unhandled exception by user

Thanks in advance