error code : There is already an open DataReader associated with this Command which must be closed first. แนะนำทีไม่รุ้จะเพิ่งที่ไหน T^T

Imports System.Data
Imports System.Data.SqlClient

Public Class Frmeitdepartment
    Dim connetionString As String
    Dim Conn As New SqlConnection
    Dim da As New SqlDataAdapter
    'Dim sc As New SqlCommand
    Dim strCon As String
    Dim ds As New DataSet
    Dim cmd As New SqlCommand(strCon, Conn)
    'Dim DR As SqlDataReader
    Private Sub Frmeitdepartment_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        strCon = "Data Source=KA4L-C62AA9DB66\SA;Initial Catalog=DBMSS;User Id=sa;Password=123;"
        Conn.ConnectionString = strCon
        If Conn.State = ConnectionState.Open Then
            Conn.Close()
        End If
        Conn.Open()

        Dim sqlcb As String
        sqlcb = "select departmentname from TbDepartment"
        Dim cmdcb As New SqlCommand(sqlcb, Conn)
        Dim DR2 As SqlDataReader = cmdcb.ExecuteReader
        If DR2.Read Then
            ComboBox1.Text = DR2("departmentname")


        End If
    End Sub



    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Dim autodepart As String
        autodepart = "SELECT max(iddepartment)+1 as iddepartment FROM Tbdepartment"
        Dim cmdauto As New SqlCommand(autodepart, Conn)
        Dim DR1 As SqlDataReader = cmdauto.ExecuteReader
        If DR1.Read Then
            TextBox1.Text = DR1("iddepartment")
            Button4.Enabled = False
            TextBox1.Enabled = False

        End If


    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim newdepart As String
        If MessageBox.Show("ยืนยันการบันทึกข้อมุล", "ยกเลิก", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) = Windows.Forms.DialogResult.OK Then
            newdepart = "insert into Tbdepartment(iddepartment,departmentname,username,pw)values('" + TextBox1.Text + "'" & ",'" + TextBox2.Text + "'" & ",'" + TextBox3.Text + "'" & ",'" + TextBox4.Text + "')"
            Dim cmdadd As New SqlCommand(newdepart, Conn)
            cmdadd.ExecuteNonQuery()
        End If


    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

        Dim sqldel As String = ("delete from Tbdepartment where namedepartment = '" & ComboBox1.Text & "'")
        Dim cmddel As New SqlCommand(sqldel, Conn) ' เป็นการเชื่อฐานข้อมูลของท่าน
        cmddel.ExecuteNonQuery()
    End Sub
End Class