SP.UI.ModalDialog.OpenPopUpPage not working in codebehind

I need to launch a InfoPath form in a Sharepoint Dialog.

Here is the Javascript:

        function openInfopath() {
            //url = document.getElementById('TextBox1').Text;
            url = 'http://devmarq/LenderDatabase/_layouts/FormServer.aspx?XmlLocation=/LenderDatabase/LenderBlog/LenderBlog-1-7.xml&ClientInstalled=true&OpenIn=Browser&DefaultItemOpen=1';
            SP.UI.ModalDialog.OpenPopUpPage(url, MyDialogCallback);
       }
          function MyDialogCallback(dialogResult, returnValue) {
            // Do stuff here
            alert('Dialog Closed');
        }

In ASP this works like a champ and displays the InfoPath form in a dialog.  Then when the dialog is closed, the alert message is displayed.
  
<a id="infoPathLink" href="#" onclick="openInfopath();return false;">Launch Infopath</a>  

However, running from codebehind, the dialog will not render:

 protected void OpenInfoPathForm(object sender, EventArgs e)
        {
            // Call launchInfoPathForm()
            Page.ClientScript.RegisterStartupScript(this.Page.GetType(), "OpenInfopath", "<script>openInfopath()</script>",false);
        }

Just to make sure I was not going crazy, I changed the javascript:

        function openInfopath() {
  alert('Should Open InfoPath in a dialog');
        }

In both cases the alert is displayed.

Why does it not work with codebehind?

Bill Behning