执行SQL Server CE命令时应用程序停止

Question

当我调试我的程序时，它工作正常，直到它：

SqlCeCommand myCommand = new SqlCeCommand("INSERT INTO dbo.Login Values ('" + userNameBox.Text + "','Admin', '" + saltedcryps + "', '" + hashedResult + "')", myConnection);
                    myCommand.ExecuteNonQuery();
                    MessageBox.Show("Thanks for registering!");
                    this.Close();

然后停止，关闭表单和除我的MDI表单之外的所有其他表单。有人可以帮忙吗？

这是我的代码：

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 System.Security.Cryptography;
using System.Data.SqlServerCe;

namespace Event_Control
{

public partial class registerScreen : Form
{
    public registerScreen()
    {
        InitializeComponent();
    }

    public static string a;

    private void registerScreen_Load(object sender, EventArgs e)
    {
    }

    private void cancelButton_Click(object sender, EventArgs e)
    {
        this.Close();
    }

    public string radioButtons()
    {
        if (userButton.Checked)
        {
            return "User";
        }
        else if (adminButton.Checked)
        {
            return "Admin";
        }
        else
        {
            MessageBox.Show("You must select an account type");
            return "error";
        }
    }

    private bool checkIfUsernameExists()
    {
        SqlCeConnection myConnection = new SqlCeConnection("Data Source=eventControl.sdf");

        try
        {
            myConnection.Open();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
        string checkuser = "select * from Login where Name = '" + userNameBox.Text + "' ";

        SqlCeCommand checkUser = new SqlCeCommand(checkuser, myConnection);

        if (checkUser.ExecuteScalar() != null)
        {
            MessageBox.Show("Username already exists");
            return false;
        }
        else
        {
            return true;
        }
    }

    private bool checkPasswordsMatch()
    {
        if (!passwordBox.Text.Equals(confirmPasswordBox.Text))
        {
            MessageBox.Show("Sorry, your passwords do not match, try again", "Password Error");
            passwordBox.Text = "";
            confirmPasswordBox.Text = "";
            return false;
        }
        else
            return true;
    }

    private bool checkUserNameEmpty()
    {
        if (userNameBox.Text == "")
        {
            MessageBox.Show("Enter a username");
            return false;
        }
        else
            return true;
    }

    private bool checkPasswordsNotEmpty()
    {
        if (passwordBox.Text == "")
        {
            MessageBox.Show("Password box is empty");
            return false;
        }
        else
            return true;
    }

    private string saltpassword(int size)
    {
        RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
        byte[] buff = new byte[size];
        crypto.GetBytes(buff);
        return Convert.ToBase64String(buff);
    }

    private string hashPassAndSalt(string passWithSalt)
    {
        HashAlgorithm hashAlg = new SHA256CryptoServiceProvider();
        byte[] bytValue = System.Text.Encoding.UTF8.GetBytes(passWithSalt);
        byte[] bytHash = hashAlg.ComputeHash(bytValue);
        string base64 = Convert.ToBase64String(bytHash);
        return base64;
    }

    private void registerButton_Click(object sender, EventArgs e)
    {
        a = radioButtons();
        string saltedcryps = saltpassword(10);
        string passWithSalt = (passwordBox.Text + saltedcryps);
        string hashedResult = hashPassAndSalt(passWithSalt);

        if (a == "Admin")
            if (checkUserNameEmpty() && checkIfUsernameExists() && checkPasswordsNotEmpty() && checkPasswordsMatch())
            {

                {

                    SqlCeConnection myConnection = new SqlCeConnection("Data Source=eventControl.sdf");
                    try
                    {
                        myConnection.Open();
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.ToString());
                    }
                    SqlCeCommand myCommand = new SqlCeCommand("INSERT INTO dbo.Login Values ('" + userNameBox.Text + "','Admin', '" + saltedcryps + "', '" + hashedResult + "')", myConnection);
                    myCommand.ExecuteNonQuery();
                    MessageBox.Show("Thanks for registering!");
                    this.Close();
                }
            }
            else
            {
            }
        else if (a == "User")
        {
            if (checkUserNameEmpty() && checkIfUsernameExists() && checkPasswordsNotEmpty() && checkPasswordsMatch())
            {
                {
                    SqlCeConnection myConnection = new SqlCeConnection("Data Source=eventControl.sdf");
                    try
                    {
                        myConnection.Open();
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.ToString());
                    }
                    SqlCeCommand myCommand = new SqlCeCommand("INSERT INTO dbo.Login Values ('" + userNameBox.Text + "','User', '" + saltedcryps + "', '" + hashedResult + "')", myConnection);
                    myCommand.ExecuteNonQuery();
                    MessageBox.Show("Thanks for registering!");
                    this.Close();
                }
            }
            else
            {
            }
        }

    }
}

就像我说的那样，它会进入If (a == "admin")部分的运行命令部分，然后停止工作。当a是User时，它也会这样做。

信息：我刚从旧程序中复制了这个程序，因为我的旧程序使用的是SQL Server，这个程序是使用SQL Server CE，所以我可以将它嵌入到程序中并在另一台计算机上使用它。它没有显示消息框，它没有向数据库添加任何信息，它只是显示我的空白MDI屏幕，当它应该在添加相关信息后返回登录屏幕

谢谢你们