错误:无法添加或更改记录，因为表中需要相关记录

当我从combox中选择Manager并输入不正确的用户名和密码时，下面的代码工作预期，错误"您不能添加或更改记录，因为表'Privileges'中需要相关记录"。如果我输入错误或正确的用户名和密码的Guest没有错误。如果我输入正确的Manager用户名和密码，则不会出现错误。错误指向cmd.ExecuteNonQuery();请问有人能帮我一下吗?

如果我从

中删除switch case Guest的整个代码

        command.CommandText = "SELECT * FROM [GuestPrivileges] WHERE STRCOMP  

那么它就会正常工作。GuestPrivileges表没有关系，它是独立的。

private void btnLogin_Click(object sender, EventArgs e)
    {
        string value = cBRoles.Text;
        switch (value)
        {
            case "Managers":
                using (var command = myCon.CreateCommand())
                {
                    command.CommandText = "SELECT * FROM [Privileges] WHERE STRCOMP(UserName, @UserName,0) = 0 AND STRCOMP(Password, @Password,0)=0";
                    command.Parameters.AddWithValue("UserName", (txtUsername.Text));
                    command.Parameters.AddWithValue("Password", (txtPassword.Text));
                    myCon.Open();
                    var reader = command.ExecuteReader();
                    {
                        if (reader.HasRows)
                        {
                            while (reader.Read())
                            {
                                txtUsername.Text = reader["UserName"].ToString();
                                txtPassword.Text = reader["Password"].ToString();
                                MainForm frm = new MainForm();
                                frm.Show();
                            }
                        }
                        else MessageBox.Show("You have entered incorrect credentials. Please try again", "error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    }
                }
                myCon.Close();
                OleDbCommand cmd = new OleDbCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "INSERT INTO LoginLogTable (UserName, LoggedInDate, LoggedInTime) VALUES (@UserName, @LoggedInDate, @LoggedInTime)";
                cmd.Parameters.AddWithValue("@UserName", txtUsername.Text);
                cmd.Parameters.AddWithValue("@LoggedInDate", DateTime.Now.ToShortDateString());
                cmd.Parameters.AddWithValue("@LoggedInTime", DateTime.Now.ToString("HH:mm"));
                cmd.Connection = myCon;
                myCon.Open();
                cmd.ExecuteNonQuery(); << error pointing here
                cmd.CommandText = "SELECT @@IDENTITY";
                int id = (int)cmd.ExecuteScalar();
                this.ID = id;
                myCon.Close();
                break;
                case "Guest":
                using (var command = myCon.CreateCommand())
                {
                    command.CommandText = "SELECT * FROM [GuestPrivileges] WHERE STRCOMP(GUserName, @GUserName,0) = 0 AND STRCOMP(GPassword, @GPassword,0)=0";
                    command.Parameters.AddWithValue("GUserName", (txtUsername.Text));
                    command.Parameters.AddWithValue("GPassword", (txtPassword.Text));
                    myCon.Open();
                    var reader = command.ExecuteReader();
                    {
                        if (reader.HasRows)
                        {
                            while (reader.Read())
                            {
                                txtUsername.Text = reader["GUserName"].ToString();
                                txtPassword.Text = reader["GPassword"].ToString();
                                ViewReport frmb = new ViewReport();
                                frmb.Show();
                            }
                        }
                        else MessageBox.Show("You have entered incorrect credentials. Please try again", "error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    }
                }
               myCon.Close();
               break;
        }
    }

Visual Studio 2010, c#， MS ACCESS 2003

提前感谢大家