Синтаксическая ошибка в инструкции INSERT - C #, Access 2013, VS Express 2013

Я пытался выяснить, почему моя программа продолжает давать мне ошибку. system.data.oledb.oledbexception(0x80040E14): Синтаксическая ошибка в инструкции INSERT INTO.

• Имя таблицы: User

• Колонки:

  Username
  AccountNumber
  FirstName
  LastName
  

Код:

namespace Library_System
{
    public partial class CreateAccountWindow : Form
    {
        OleDbConnection connect = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data         Source=C:\Users\Jc\Documents\Visual Studio 2013\Projects\Library System\Library     System\LibrarySystemDatabase.accdb;Persist Security Info=False;");
    OleDbCommand command = new OleDbCommand();
    //OleDbDataReader reader;

    public CreateAccountWindow()
    {
        InitializeComponent();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        string Username = "", AccountNumber = "", FirstName = "", LastName = "";
        //int Borrowed = 0;
        bool hasValue1 = false, hasValue2 = false, hasValue3 = false, hasValue4 = false;
        if (textBox1.Text != "")
        {
            label1.Hide();
            Username = textBox1.Text;
            hasValue1 = true;
        }
        else
        {
            label1.Show();
            label1.Text = "Required";
        }

        if (textBox10.Text != "")
        {
            label21.Hide();

            AccountNumber = textBox8.Text;
            hasValue2 = true;
        }
        else
        {
            label21.Show();
            label21.Text = "Required";
        }

        if (textBox8.Text != "")
        {
            label13.Hide();

            FirstName = textBox10.Text;
            hasValue3 = true;
        }
        else
        {
            label13.Show();
            label13.Text = "Required";
        }

        if (textBox7.Text != "")
        {
            label12.Hide();
            label12.Text = "Required";
            LastName = textBox7.Text;
            hasValue4 = true;
        }
        else
        {
            label12.Show();
            label12.Text = "Required";
        }

        if (hasValue1 || hasValue2 || hasValue3 || hasValue4)
        {
            try
            {
                connect.Open();
                OleDbCommand command = new OleDbCommand();
                command.Connection = connect;
                command.CommandText = "insert into User (Username,AccountNumber,FirstName,LastName) values ('" + Username + "','" + AccountNumber + "','" + FirstName + "','" + LastName + "')";
                command.ExecuteNonQuery();
                MessageBox.Show("REGISTRATION COMPLETE !!", "DONE");
                connect.Close();
            }
            catch (Exception ex)
            {
                connect.Close();
                MessageBox.Show("Error:"+ex.ToString());
            }
        }
    }
}