Print Blank Page while Print Preview shows the page correct

Question

 Hi,
I am trying to print data from the printer button in the top left of Print Preview window from c#, but it gives blank page.

Below is the code  

// Result of the Event 'PrintPage'
        private void prnDocument_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
        {
        leftMargin = (int)e.MarginBounds.Left;
        rightMargin = (int)e.MarginBounds.Right;
        topMargin = (int)e.MarginBounds.Top;
        bottomMargin = (int)e.MarginBounds.Bottom;
        InvoiceWidth = (int)e.MarginBounds.Width;
        InvoiceHeight = (int)e.MarginBounds.Height;

            if (!ReadInvoice)
            {
                ReadInvoiceData();


                SetInvoiceData(e.Graphics, e); // Draw Invoice Data
            }

            ReadInvoice = true;

        }

private void DisplayInvoice()
    {
            prnPreview.Size = new System.Drawing.Size(700, 800);
            try
            {
                prnPreview.Document = prnDocument;
               prnPreview.ShowDialog();

            }
            catch (Exception e)
            {
                MessageBox.Show(e.ToString());
            }
        }

private void btnPreview_Click(object sender, System.EventArgs e)
    {
            ReadInvoice = false;
            DisplayInvoice(); // Print Preview
         }

public frmOrder()
    {
        InitializeComponent();
        this.prnDialog = new System.Windows.Forms.PrintDialog();
        this.prnPreview = new System.Windows.Forms.PrintPreviewDialog();
        this.prnDocument = new System.Drawing.Printing.PrintDocument();
        // The Event of 'PrintPage'
        prnDocument.PrintPage += new System.Drawing.Printing.PrintPageEventHandler(prnDocument_PrintPage);

    }

 

private void SetInvoiceData(Graphics g, System.Drawing.Printing.PrintPageEventArgs e)
        {// Set Invoice Table:
            string FieldValue = "";
            int CurrentRecord = 0;
            int RecordsPerPage = 5; // twenty items in a page
            decimal Amount = 0;
            bool StopReading = false;

            // Set Table Head:
            int xProductID = leftMargin;
            CurrentY = CurrentY + InvoiceFontHeight-10;
            g.DrawString("Τιμολόγιο", InvoiceFontBold, BlackBrush, xProductID, CurrentY);

            int xProductName = xProductID+ (int)g.MeasureString("Invoice", InvoiceFont).Width + 40;
            g.DrawString("Ημέρες", InvoiceFontBold, BlackBrush, xProductName, CurrentY);

            int xUnitPrice = xProductName  + (int)g.MeasureString("Days", InvoiceFont).Width + 10;
            g.DrawString("Σύνολο", InvoiceFontBold, BlackBrush, xUnitPrice, CurrentY);

            int xQuantity = xUnitPrice  + (int)g.MeasureString("Total", InvoiceFont).Width + 30;
            g.DrawString("Αιτιολογία", InvoiceFontBold, BlackBrush, xQuantity, CurrentY);
            AmountPosition= xQuantity + (int)g.MeasureString("Σύνολο", InvoiceFont).Width + 170;
            // Set Invoice Table:
            CurrentY = CurrentY + InvoiceFontHeight + 8;
               while (CurrentRecord < RecordsPerPage)
                    {
                        FieldValue = rdr["InvoiceNo"].ToString();
                        g.DrawString(FieldValue, InvoiceFont, BlackBrush, xProductID, CurrentY);
                        FieldValue = rdr["Days Rented"].ToString();
                        g.DrawString(FieldValue, InvoiceFont, BlackBrush, xProductName, CurrentY);
                        FieldValue = String.Format("{0:0.00}", rdr["Period amount"]);
                        g.DrawString(FieldValue, InvoiceFont, BlackBrush, xUnitPrice, CurrentY);
                        FieldValue = rdr["Reason"].ToString();
                        g.DrawString(FieldValue, InvoiceFont, BlackBrush, xQuantity, CurrentY);
                        CurrentY = CurrentY + InvoiceFontHeight;

                        if (!rdr.Read())
                        {
                            StopReading = true;
                            break;
                        }

                        CurrentRecord++;
                    }
           if (CurrentRecord < RecordsPerPage)
            { e.HasMorePages = false; }
            else
            { e.HasMorePages = true;}


            if (StopReading)
            {   rdr .Close();
                con.Close();
                SetInvoiceTotal(g);
            }

            g.Dispose();
        }

 Thank you,

John