asp.net ajax postback problem

I have a link control inside UpdatePanel and it opens a dom window defined in the css class. It works the first time, but after postback, it no longer works. It opens a new window instead of the dom windoer. If I moved the asp:HyperLink outside the UpdatePanel, it works fine. However, I need this to be within the UpdatePanel because it is a dynamic link.

                              <ContentTemplate>
                            <asp:UpdatePanel>

<asp:HyperLink ID="lnkPay" runat="server" CssClass="open_popup" text="Click to see" />
                          ...