La barra de progreso supera el valor máximo

La barra de progreso excede el valor máximo cuando se usa la operación ++ para incrementar el valor. En el siguiente código, tengo un conjunto de registros que tiene un tamaño de 6004 cuando llega al bucle, se las arregla para llegar a 6006 a pesar de que puse una declaración if para atrapar cuando alcanza el valor ++ para restablecer la barra de progreso a cero y también ocultar el panel.

    invoiceRecord = (SageDataObject240.InvoiceRecord)_workSpace.CreateObject(Resources.InvoiceRecord);


    pnlProgress.Visible = true;
    progBarSelectInvoices.Value = 0;
    progBarSelectInvoices.Maximum = invoiceRecord.Count;

    List<EdiInvoice> selectedInvoices = new List<EdiInvoice>();
    EdiInvoice invoice;

    DateTime fromDate = chkEnableFromDatePicker.Checked ? dtpFrom.Value.Date : DateTime.MinValue;
    DateTime toDate = chkEnableToDatePicker.Checked ? dtpTo.Value.Date : DateTime.MaxValue;
    int invoiceCount = 0;
    int progressCount = 0;
  int progresbarValue = 0;          
    int maxCount = invoiceRecord.Count + 1;
    while (invoiceRecord.MoveLast())
    {
        progresbarValue = progBarSelectInvoices.Value++;
        bool isPosted = (SDOHelper.Read<sbyte>(invoiceRecord, Resources.POSTED_CODE) == 1);

        if (isPosted)
        {
            int invoiceNo = SDOHelper.Read<int>(invoiceRecord, Resources.INVOICE_NUMBER);
            string invoiceCustomerReference = SDOHelper.Read<string>(invoiceRecord, Resources.ACCOUNT_REF);
            bool isValidCustomerReference = (invoiceCustomerReference == _selectedCustomer.Reference || _selectedCustomer.IncludeBranchInvoices && _selectedCustomer.BranchCodes.ContainsKey(invoiceCustomerReference));

            sbyte invoiceTypeCode = SDOHelper.Read<sbyte>(invoiceRecord, Resources.INVOICE_TYPE_CODE);
            bool isValidType = invoiceTypeCode >= 0 && invoiceTypeCode <= 5;

            string notes1 = SDOHelper.Read<string>(invoiceRecord, "NOTES_1");
            bool isExported = notes1.Length > 2 && notes1.Substring(0, 3).Equals("EDI", StringComparison.CurrentCultureIgnoreCase);

            DateTime invoiceDate = SDOHelper.Read<DateTime>(invoiceRecord, "INVOICE_DATE");
            bool isInDateRange = invoiceDate >= fromDate && invoiceDate <= toDate;

            if (isValidCustomerReference && isValidType && (!isExported || chkIncludeAlreadyExportedInvoices.Checked) && isInDateRange)
            {
                invoice = new EdiInvoice();
                invoice.Customer = string.Format("({0}), {1}", invoiceCustomerReference, SDOHelper.Read<string>(invoiceRecord, Resources.NAME));
                invoice.InvoiceNumber = invoiceNo;
                invoice.Date = SDOHelper.Read<DateTime>(invoiceRecord, "INVOICE_DATE").ToString("dd/MM/yyyy");
                invoice.Type = GetInvoiceOrCredit(invoiceTypeCode);
                invoice.DeliveryAddress = SDOHelper.Read<string>(invoiceRecord, Resources.DEL_ADDRESS_1);
                invoice.Nett = SDOHelper.Read<double>(invoiceRecord, Resources.BASE_TOT_NET) + SDOHelper.Read<double>(invoiceRecord, Resources.BASE_CARR_NET);
                invoice.Vat = SDOHelper.Read<double>(invoiceRecord, Resources.BASE_TOT_TAX) + SDOHelper.Read<double>(invoiceRecord, Resources.BASE_CARR_TAX);

                selectedInvoices.Add(invoice);
            }
        }
           invoiceCount = invoiceRecord.Count;
           progressCount = progBarSelectInvoices.Value;
        if (progressCount++ == maxCount || progressCount==invoiceCount )
        {
            progBarSelectInvoices.Value = 0;
            progressCount = 0;
            pnlProgress.Visible = false;
            Application.DoEvents();
        }
        else

        {
            progBarSelectInvoices.Value++;
            progressCount= progBarSelectInvoices.Value++;
        }
        Application.DoEvents();