问主菜单加载时未分配正确的权限(C#)

EN

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.Data.SqlClient;
using DBL;

namespace Interfaces
{
    public partial class frmLogin : Form
    {
        public frmLogin()
        {
            InitializeComponent();
        }

        public string UserID;
        public string Password;
        public string Role;


        private void btnLogin_Click(object sender, EventArgs e)
        {

            String SQL = "SELECT * FROM LoginInfo";

            string connectionString;
            SqlConnection con;
            connectionString = @"Data Source=DESKTOP-U9V5QGE\CL_HNDCSE_86_16;Initial Catalog=UNIMAP_WAD;Integrated Security=True";
            con = new SqlConnection(connectionString);
            con.Open();

            SqlCommand comm = new SqlCommand(SQL, con);
            SqlDataReader sqlDReader = comm.ExecuteReader();

            UserID = txtUserID.Text;
            Password = txtPassword.Text;


            while (sqlDReader.Read())
            {
                Role = sqlDReader["Role"].ToString();
            }

            if (UserID == sqlDReader["UserID"].ToString() && Password == sqlDReader["Password"].ToString())
            {

                con.Close();

                if (Role == "SuperAdmin")
                {
                    CurrentCredentials.LoggedInUID = UserID;
                    CurrentCredentials.LoggedInRole = Role;

                    frmMainMenu objmainmenu = new frmMainMenu();
                    objmainmenu.Show();


                }
                else if (Role == "Admin")
                {
                    CurrentCredentials.LoggedInUID = UserID;
                    CurrentCredentials.LoggedInRole = Role;

                    frmMainMenu objmainmenu = new frmMainMenu();
                    objmainmenu.Show();

                    objmainmenu.credentialsToolStripMenuItem.Visible = false;
                }
                else if (Role == "StudentCoordinator")
                {
                    CurrentCredentials.LoggedInUID = UserID;
                    CurrentCredentials.LoggedInRole = Role;

                    frmMainMenu objmainmenu = new frmMainMenu();
                    objmainmenu.Show();

                    objmainmenu.credentialsToolStripMenuItem.Visible = false;
                    objmainmenu.lecturerToolStripMenuItem.Visible = false;
                }

                else if (Role == "Lecturer")
                {
                    CurrentCredentials.LoggedInUID = UserID;
                    CurrentCredentials.LoggedInRole = Role;

                    frmMainMenu objmainmenu = new frmMainMenu();
                    objmainmenu.Show();

                    objmainmenu.credentialsToolStripMenuItem.Visible = false;
                    objmainmenu.studentToolStripMenuItem.Visible = false;

                }

                else if (Role == "Student")
                {
                    CurrentCredentials.LoggedInUID = UserID;
                    CurrentCredentials.LoggedInRole = Role;

                    frmMainMenu objmainmenu = new frmMainMenu();
                    objmainmenu.Show();

                    objmainmenu.credentialsToolStripMenuItem.Visible = false;
                    objmainmenu.lecturerToolStripMenuItem.Visible = false;

                }
                else
                {
                    MessageBox.Show("Invalid credentials", "ERROR!", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }

            }
            else
            {
                MessageBox.Show("Invalid credentials", "ERROR!", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }


        }


    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using DBL;

namespace DBL
{
    public static class CurrentCredentials
    {
        private static string _LoggedInUID;
        private static string _LoggedInRole;


        public static String LoggedInUID
        {

            get
            {
                return _LoggedInUID;
            }
            set
            {
                _LoggedInUID = value;
            }

        }

        public static String LoggedInRole
        {
            get
            {
                return _LoggedInRole;
            }
            set
            {
                _LoggedInRole = value;
            }

        }

    }
}

//error

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll

//received from the line
if (UserID == sqlDReader["UserID"].ToString() && Password == sqlDReader["Password"].ToString())