ทำโปรแกรมเพิ่มลบแก้ไขLINQ ฟอร์มแรกได้ดีไม่มีปัญหา พอทำฟอร์มที่ 2 โค้ดใช้ไม่ได้เฉยเลยครับ

Option Explicit On
Option Strict On

Public Class frm_customer
    Dim db As New dbdokmaiDataContext()

    Private Sub frm_customer_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ShowCustomers()
        FormatDgv_customers()
        formready()
        cbbadd()

    End Sub

    Private Sub ShowCustomers()
        Dim cs = From c In db.customers
                 Order By c.cus_id
                 Select New With {
                     .cus_id = c.cus_id,
                     .cus_type = c.cus_type,
                     .cus_title = c.cus_title,
                     .cus_name = c.cus_name,
                     .cus_sur = c.cus_sur,
                     .cus_age = c.cus_age,
                     .cus_phone = c.cus_phone}
        dgv_cus.DataSource = cs.ToList()
    End Sub

    Private Sub FormatDgv_customers()
        With dgv_cus
            If .RowCount > 0 Then
                .Columns(0).HeaderText = "รหัส"
                .Columns(1).HeaderText = "ประเภท"
                .Columns(2).HeaderText = "คำนำหน้า"
                .Columns(3).HeaderText = "ชื่อ"
                .Columns(4).HeaderText = "นามสกุล"
                .Columns(5).HeaderText = "อายุ"
                .Columns(6).HeaderText = "เบอร์โทรศัพท์"

                .Columns(0).Width = 50
                .Columns(1).Width = 70
                .Columns(2).Width = 50
                .Columns(3).Width = 90
                .Columns(4).Width = 90
                .Columns(5).Width = 90
                .Columns(6).Width = 90

            End If
        End With
    End Sub

    Private Sub formready()
        cbb_type.Enabled = False
        txt_id.ReadOnly = True
        cbb_title.Enabled = False
        txt_name.ReadOnly = True
        txt_sur.ReadOnly = True
        txt_age.ReadOnly = True
        txt_phone.ReadOnly = True
        txt_address.ReadOnly = True
        txt_roc.ReadOnly = True
        cbb_lost.Enabled = False

        btn_saveadd.Enabled = False
        btn_edit.Enabled = False

    End Sub


    Private Sub cbbadd()

        cbb_type.Items.Add("ทั่วไป")
        cbb_type.Items.Add("บัตรทอง(หลักประกันสุขภาพถ้วนหน้า)")
        cbb_type.Items.Add("ประกันสังคมโรงพยาบาล1")
        cbb_type.Items.Add("ประกันสังคมโรงพยาบาล2")
        cbb_type.Items.Add("ประกันสังคมโรงพยาบาล3")
        cbb_type.Items.Add("ประกันสังคมโรงพยาบาล4")
        cbb_type.SelectedIndex = 0

        cbb_lost.AutoCompleteMode = AutoCompleteMode.SuggestAppend
        cbb_lost.AutoCompleteSource = AutoCompleteSource.ListItems
        cbb_lost.Items.Clear()
        cbb_lost.Items.Add("phenotiazine")
        cbb_lost.Items.Add("sulfonamide")
        cbb_lost.Items.Add("halathane")
        cbb_lost.Items.Add("phenyltoin")
        cbb_lost.Items.Add("Isoniazid")
        cbb_lost.Items.Add("nitrofurantoin ")

        cbb_title.AutoCompleteMode = AutoCompleteMode.SuggestAppend
        cbb_title.AutoCompleteSource = AutoCompleteSource.ListItems
        cbb_title.Items.Clear()
        cbb_title.Items.Add("ด.ช.")
        cbb_title.Items.Add("ด.ญ.")
        cbb_title.Items.Add("นาย.")
        cbb_title.Items.Add("นางสาว.")
        cbb_title.Items.Add("นาง")

    End Sub

  

    Private Sub ClearAllData()
        cbb_type.Text = ""
        txt_id.Text = ""
        cbb_title.Text = ""
        txt_name.Text = ""
        txt_sur.Text = ""
        txt_age.Text = ""
        txt_phone.Text = ""
        txt_address.Text = ""
        txt_roc.Text = ""
        cbb_lost.Text = ""
        
    End Sub

    Private Function CheckcustomersData() As Boolean
        CheckcustomersData = False
        If (cbb_title.Text.Trim() = "") Or (txt_name.Text.Trim() = "") Or (txt_sur.Text.Trim() = "") Then
            '(txt_id.Text.Trim() = "") Or
            MessageBox.Show("กรุณาป้อนข้อมูลลูกค้าให้ครบ !!!", "ข้อผิดพลาด")
            cbb_title.Focus()
            Return False
        Else
            Return True
        End If
    End Function

    Private Sub dgv_cus_CellMouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellMouseEventArgs) Handles dgv_cus.CellMouseUp
        If e.RowIndex = -1 Then Exit Sub
        With dgv_cus
            txt_id.Text = .Rows.Item(e.RowIndex).Cells(0).Value.ToString()
            txt_name.Text = .Rows.Item(e.RowIndex).Cells(1).Value.ToString()
            txt_phone.Text = .Rows.Item(e.RowIndex).Cells(2).Value.ToString()
            txt_id.Focus()
            txt_id.SelectAll()
        End With
    End Sub

Option Explicit On
Option Strict On

Public Class frm_doctor
    Dim db As New dbdokmaiDataContext()

    Private Sub frm_doctor_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        btn_saveadd.Enabled = False
        btn_edit.Enabled = False
        txt_id.ReadOnly = True
        txt_name.ReadOnly = True
        txt_phone.ReadOnly = True
        ShowCustomers()
        FormatDgv_doctor()


    End Sub


    Private Sub ShowCustomers()
        Dim cs = From c In db.doctors
                 Order By c.doc_id
                 Select New With {
                     .doc_id = c.doc_id,
                     .doc_name = c.doc_name,
                     .doc_phone = c.doc_phone
                 }
        dgv_doc.DataSource = cs.ToList()

    End Sub

    Private Sub FormatDgv_doctor()
        With dgv_doc
            If .RowCount > 0 Then
                .Columns(0).HeaderText = "รหัสแพทย์"
                .Columns(1).HeaderText = "ชื่อ-สกุล"
                .Columns(2).HeaderText = "เบอร์โทรศัพท์"

                .Columns(0).Width = 70
                .Columns(1).Width = 200
                .Columns(2).Width = 90
            End If
        End With
    End Sub


    Private Sub btn_saveadd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_saveadd.Click
        Dim result = CheckdoctorsData()
        If result = True Then
            Dim c As New doctor()
            'c.doc_id = CInt(txt_id.Text.Trim())
            c.doc_name = txt_name.Text.Trim()
            c.doc_phone = txt_phone.Text()

            If MessageBox.Show("คุณต้องการเพิ่มข้อมูลแพทย์ ใช่หรือไม่?", "คำยืนยัน", MessageBoxButtons.YesNo) = Windows.Forms.DialogResult.Yes Then
                txt_id.Text = ""
                db.doctors.InsertOnSubmit(c)
                db.SubmitChanges()
                ClearAllData()
                ShowCustomers()
                btn_add.Enabled = True
                btn_fedit.Enabled = True
                btn_edit.Enabled = False
                btn_del.Enabled = True
                btn_showall.Enabled = True
                txt_find.Enabled = True

                btn_saveadd.Enabled = False
                MessageBox.Show("เพิ่มข้อมูลแพทย์ เรียบร้อยแล้ว", "ผลการทำงาน")


            End If
        End If

    End Sub

    Private Sub dgv_doc_CellMouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellMouseEventArgs) Handles dgv_doc.CellMouseUp
        If e.RowIndex = -1 Then Exit Sub
        With dgv_doc
            txt_id.Text = .Rows.Item(e.RowIndex).Cells(0).Value.ToString()
            txt_name.Text = .Rows.Item(e.RowIndex).Cells(1).Value.ToString()
            txt_phone.Text = .Rows.Item(e.RowIndex).Cells(2).Value.ToString()
            txt_id.Focus()
            txt_id.SelectAll()
        End With
    End Sub