getContentAsPDF is working in visualforce pages but not working in production sites?

How to create a attacment from visualforce site? I have created godaddy domain in our salesforce and given certificates for domain. for this domain i have access to view the visuaforce pages.I have created visualforce page as renderas"PDF" and i am calling from visualforce page attachment is created successfully but when i run the page from site its not created the attachment. i have given access the visualforce page andenter code here apex controller and also i have given access to object and fields. see below code.

account acc =[select id,name from account where id='myrecordid'];
pagereference pgref = page.mypdfpage;
pageref.getParameters().put('id',acc.Id);
pageref.setRedirect(false);
blob body;
body= pageref.getContentAsPDF();
Attachment attach = new Attachment();
attach.body = body;
attach.Name = 'myattachpage';
attach.Isprivate = false;
attach.ParentId = acc.Id;
attach.ContentType = 'pdf';
insert attach;