I have created a List JS button in Opportunity Page > Quote Related List to generate Quote PDF for the selected Quote record. I get PdfOverlay undefined and after that a message is displayed "Cannot read Property 'dialog' of undefined. Below is my code:-

{!REQUIRESCRIPT("/soap/ajax/14.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/14.0/apex.js")}

records = {!GETRECORDIDS($ObjectType.Quote)};
alert('records > ' + records);
var selectedRecords = [records];
alert('selectedRecords>' + selectedRecords);


var pdfOverlay = QuotePDFPreview.quotePDFObjs['quotePDFOverlay'];

alert('pdfOverlay > ' + pdfOverlay);

pdfOverlay.dialog.buttonContents = '<input value=\"Save to Quote\"  class=\"btn\" name=\"save\" onclick=\"QuotePDFPreview.getQuotePDFObject(\'quotePDFOverlay\').savePDF(\'0\',\'0\');\" title=\"Save to Quote\" type=\"button\" /><input value=\"Save and Email Quote\"  class=\"btn\" name=\"saveAndEmail\" onclick=\"QuotePDFPreview.getQuotePDFObject(\'quotePDFOverlay\').savePDF(\'1\');\" title=\"Save and Email Quote\" type=\"button\" /><input value=\"Cancel\"  class=\"btn\" name=\"cancel\" onclick=\"QuotePDFPreview.getQuotePDFObject(\'quotePDFOverlay\').close();\" title=\"Cancel\" type=\"button\" />';



 //change this to use the correct template for your business/environment!! 
pdfOverlay.summlid = '0EH90000000Gdtu'; 

 pdfOverlay.setSavable(true); 

 //change this to use the quote id 
pdfOverlay.setContents('/quote/quoteTemplateDataViewer.apexp?id={!Quote.Id}','quote/quoteTemplateHeaderData.apexp?id={!Quote.Id}'); 

 pdfOverlay.display();

Kindly suggest some soln.