Getting blank graphic page (intermittently) when printing a html document using Windows Forms Web Browser control

I have developped a Web application to display  html documents (mixed text and graphics).  The application includes some print functionaly (Print / Prewview). The MS Webbrowser Print Template mechanism are used for formatting (with custom  header/footer)  the printed pages.  The Print functionality in the Web app will call API methods provided by a client component (.NET COM  DLL) on the client side to print the  html document displayed in IE 8.

In the client component codes  (implemented with C# and using Web browser control from .NET Framework 3.5),  I have implemented a function to print a html document (mixed text and graphics)

by calling  Web browser  control ‘Navigate’ method to load html document (invisible)  and relying on Web browser control event to indicate when the  html document loading process is complete  before calling Web browser control  ExecWB  method  to  initiate the printing process .

The codes are as follows :

// Create a WebBrowser instance.
            System.Windows.Forms.WebBrowser webBrowserForPrinting = new System.Windows.Forms.WebBrowser();
            System.Text.Encoding encoding = System.Text.Encoding.UTF8;
            string nullStr = "";
            object nullObjStr = nullStr;
            byte[] nullArrayObj = null;
            byte[] postData = encoding.GetBytes(keyList);
            string addHeaders = "Content-Type: application/x-www-form-urlencoded" + "\n" + "\r";
            object tplObjStr = templateURL;
                      
            // Load html web page
            if (keyList == null || keyList.Length == 0)
                webBrowserForPrinting.Navigate(target, nullStr, nullArrayObj, nullStr);
            else
                webBrowserForPrinting.Navigate(target, nullStr, postData, addHeaders);
            // Waiting until the web page download process is completed
            Application.UseWaitCursor = true;
            while (webBrowserForPrinting.ReadyState != WebBrowserReadyState.Complete)
            {
                Application.DoEvents();
            }
                                 IWebBrowser2 browser = (IWebBrowser2)webBrowserForPrinting.ActiveXInstance;
            // Start printing ...
           
                       
            switch (printOption)
            {
                case 1:
                    browser.ExecWB(OLECMDID.OLECMDID_PRINTPREVIEW, OLECMDEXECOPT.OLECMDEXECOPT_DODEFAULT, ref tplObjStr, ref nullObjStr);
                    break;
                case 2:
                    browser.ExecWB(OLECMDID.OLECMDID_PRINT, OLECMDEXECOPT.OLECMDEXECOPT_DONTPROMPTUSER, ref tplObjStr, ref nullObjStr);
                    break;
                case 3:
                    browser.ExecWB(OLECMDID.OLECMDID_PRINT, OLECMDEXECOPT.OLECMDEXECOPT_PROMPTUSER, ref tplObjStr, ref nullObjStr);
                    break;
                default :
                    browser.ExecWB(OLECMDID.OLECMDID_PRINT, OLECMDEXECOPT.OLECMDEXECOPT_PROMPTUSER, ref tplObjStr, ref nullObjStr);
                    break;
            }
            // Terminate web browser control instance
            webBrowserForPrinting.Dispose();I have experienced some unexpected results when printing a simple html document.  The correct result should be two pages :one text page and one  graphic page.  But sometimes I've got one text page and two blank pages.

I have investigated the IE temp files (generated by Web browser when html doc is loaded completely) for two cases :

(1)  No missing graphic (an emf file is generated by Web browser to store the graphic bitmap image)  :  The following parameter is added to <OBJECT> tag in  IE temp html file :  PARAM NAME="_Snapshot_EMF" VALUE=".......GN1FX1Q2.emf">

(2) Missing graphic (blank page), no emf file is generated :  The following parameter is added to <OBJECT> tag in  IE temp html file  <PARAM NAME="_Snapshot_EMF" VALUE="_ZERO">

For this type of the issue, I assume there might be caused by some network latency/ timing issue that affects IE Web browser behavior because Web browser need time to get graphic data from the Web application server and convert to bitmap.

However,  even when I add some time delay (5 sec) in the codes after the html document is loaded completely to Web browser as follows :

            Application.UseWaitCursor = true;
            while (webBrowserForPrinting.ReadyState != WebBrowserReadyState.Complete)
            {
                Application.DoEvents();
            }
     Thread.Sleep(5000);
.................................        The issue still cannot be resolved.

Have anyone experienced similar issues?

Is this .NET Web browser control issue?

How do we resolve this issue?

Any ideas / comments / suggestions  are greatly appreciated.

Thanks,

Kevin Ton