打印文件时出错，但打印网页时不出错

使用InternetExplorer对象，我可以打印一个网页。但是当我尝试打印文件时，我得到以下错误:

System.Runtime.InteropServices.COMException:被调用的对象已断开连接

我做错了什么?

下面是代码(感谢这个答案):

public class Program
{
    static void main(string[] args)
    {
        // this works
        (new HTMLPrinter()).Print("www.google.com");
        // this brings up the file in a browser 
        // but then throws an exception when checking print status!
        (new HTMLPrinter()).Print("C:'Temp'test.html");  
    }
}
public class HTMLPrinter
{
    private bool documentLoaded;
    private bool documentPrinted;
    private void ie_DocumentComplete(object pDisp, ref object URL)
    {
        documentLoaded = true;
    }
    private void ie_PrintTemplateTeardown(object pDisp)
    {
        documentPrinted = true;
    }
    public void Print(string htmlFilename)
    {
        documentLoaded = false;
        documentPrinted = false;
        InternetExplorer ie = new InternetExplorerClass();
        ie.DocumentComplete += new DWebBrowserEvents2_DocumentCompleteEventHandler(ie_DocumentComplete);
        ie.PrintTemplateTeardown += new DWebBrowserEvents2_PrintTemplateTeardownEventHandler(ie_PrintTemplateTeardown);
        object missing = Missing.Value;
        ie.Navigate(htmlFilename, ref missing, ref missing, ref missing, ref missing);
        // An exception is thrown at 
        // SHDocVw.InternetExplorerClass.QueryStatusWB
        // only when trying to print a file!
        // Exception details: System.Runtime.InteropServices.COMException:
        // The object invoked has disconnected from its client.
        while (!documentLoaded && ie.QueryStatusWB(OLECMDID.OLECMDID_PRINT) != OLECMDF.OLECMDF_ENABLED)
            Thread.Sleep(100);        
        ie.ExecWB(OLECMDID.OLECMDID_PRINT, OLECMDEXECOPT.OLECMDEXECOPT_DONTPROMPTUSER, ref missing, ref missing);
        while (!documentPrinted)
            Thread.Sleep(100);
        ie.DocumentComplete -= ie_DocumentComplete;
        ie.PrintTemplateTeardown -= ie_PrintTemplateTeardown;
        ie.Quit();
    }
}