VB.net combobox เวลาเลือกเปลี่ยนข้อมูลแล้วมัน Error ตรงส่วน ผมผิดตรงไหนเหรอครับ

   Private Sub ShowDataCombobox()

        If ComboCondition.Text = "Terminal" Then
            sb = New StringBuilder()
            sb.Append("SELECT * FROM tTerminal")
            Dim sqlIni As String
            sqlIni = sb.ToString()

            RemoveHandler ComboDetail.SelectedValueChanged, AddressOf ComboDetail_SelectedIndexChanged
            com = New SqlCommand()
            With com
                .CommandText = sqlIni
                .CommandType = CommandType.Text
                .Connection = Conn
                dr = .ExecuteReader()
            End With

            If dr.HasRows Then
                Dim dttTerminal As DataTable
                dttTerminal = New DataTable()
                dttTerminal.Load(dr)

                With ComboDetail
                    .BeginUpdate()
                    .DisplayMember = "C_Name"
                    .ValueMember = "L_ID"
                    .DataSource = dttTerminal
                    .EndUpdate()
                End With

                dr.Close()
                AddHandler ComboDetail.SelectedValueChanged, AddressOf ComboDetail_SelectedIndexChanged

                ComboDetail.ContextMenu = New ContextMenu()
            End If

ElseIf ComboCondition.Text = "Department" Then
            sb = New StringBuilder()
            'sb.Append("SELECT {FN Concat({FN Concat(c_code,' : ')},substring(c_name,1,30))} As test FROM cPost")
            sb.Append("SELECT * FROM cPost")
            Dim sqlIni As String
            sqlIni = sb.ToString()
            RemoveHandler ComboDetail.SelectedValueChanged, AddressOf ComboDetail_SelectedIndexChanged

            com = New SqlCommand()
            With com
                .CommandText = sqlIni
                .CommandType = CommandType.Text
                .Connection = Conn
                dr = .ExecuteReader()
                If dr.HasRows Then
                    dtcPost = New DataTable
                    dtcPost.Load(dr)
                    With ComboDetail
                        .BeginUpdate()
                        .DisplayMember = "C_Name"
                        .ValueMember = "C_Code"
                        .DataSource = dtcPost
                        .EndUpdate()
                    End With
                End If

                dr.Close()
                AddHandler ComboDetail.SelectedValueChanged, AddressOf ComboDetail_SelectedIndexChanged

                ComboDetail.ContextMenu = New ContextMenu()
            End With
        End If
    End Sub