popup a page by clicking on a hyperlink after user confirms action.

I have a page that displays a list of question. Next to each question is an asp:HyperLink 'Add Note'.  When the user clicks on the Add Note link a confirmation message is displayed telling them that unsubmitted work will be lost.  If they answer OK then a page should popup using the window.open method so I can control the page size and apperance.  I tried using the followin code:
<asp:HyperLink ID="HyperLink1" runat="server" Target="_blank" NavigateUrl="javascript:window.open('','VOEAddNote.aspx?OrderID=Request.QueryString['OrderID'].ToString() &VOEquestionID=DataBinder.Eval(Container.DataItem, 'VOEquestionID')', 'width=200, height=400');" onclick="return confirm('Answers that have not been submitted will be cleared.');">Add Note</asp:HyperLink> The confirmation message displays but after clicking ok, i get an error that t ...