C# how to insert and search data on testbox within database

 SubjectName
Accounting
Biology
Bussiness
Computer Science
Computing
English
Law
Maths

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.' on program.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using MySql.Data.MySqlClient;


namespace ProjectInterface
{
    public partial class Concept : Form
    {

        MySqlConnection con = new MySqlConnection("server=localhost;Database=databse;Port = 3306; User ID = root; Password = password123");
        MySqlCommand cmd = new MySqlCommand();

        public Concept()
        {
            InitializeComponent();
        }



        private void btnNextC_Click(object sender, EventArgs e)
        {
            con.Open();

      

            string newcon = "Insert into tutorials(TutorialName) VALUES ('" + txtTuName.Text + " ')";

            MySqlCommand cmd = new MySqlCommand(newcon, con);
            cmd.ExecuteNonQuery();



            this.Hide();
            Home home = new Home();
            home.Show();

            //next - go t oquestionnaire page
            //this.Hide();
            //Questionnaire q = new Questionnaire();
            //q.Show();

        }
        private void btnCancelC_Click(object sender, EventArgs e)
        {
            //cancel button - go back to home page.
            this.Hide();
            Home home = new Home();
            home.Show();
        } 

        private void Concept_Load(object sender, EventArgs e)
        {

        }

        private void txtSubject_TextChanged(object sender, EventArgs e)
        {
            con.Open();
  
            
            MySqlCommand cmd = new MySqlCommand("SELECT  SubjectName From databse.subject WHERE SubjectName LIKE @name",con);
            cmd.Parameters.Add(new MySqlParameter("@name", "%" + txtSubject.Text + "%"));

            MySqlDataReader dr = cmd.ExecuteReader();

            AutoCompleteStringCollection subjectColl = new AutoCompleteStringCollection();

            while (dr.Read()) { 
                subjectColl.Add(dr.GetString(0));
             }
            
            txtSubject.AutoCompleteCustomSource = subjectColl;
            con.Close();


        }

   }