Click button event is not firing inside the Ajax Modal popup

I have an Ajax Modal popup in my page that is going to open by clicking on Edit button. I also have some code behind that is filling value in the popup textboxes. My problem is that by clicking on the Edit button the popup is going to show but the btnEdit_Click that is in the backend is not firing.

This is my aspx code:
<%-- Start of popup--%> <table border="0" cellpadding="0" cellspacing="0"> <tr><td> </td></tr> <tr> <td> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <asp:DropDownList ID="ddlPartnerList" runat="server" CssClass="roundedbox" OnSelectedIndexChanged="ddlPartnerList_SelectedIndexChanged" AutoPostBack="true"></asp:DropDownList> <asp:Butto ...