Update panel - multiview - controls not getting fired

HI,

I am using ASP.NET 4.0 and i have placed a update panel. The page has 2 views. 

I have button and dropdown events in the views. I have used the below code:

<asp:UpdatePanel ID="upd1" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true"><ContentTemplate><asp:MultiView ID="Mul1" runat="server" ActiveViewIndex="0"><asp:View ID="View1" runat="server"><table><tr> <td><asp:ImageButton ID="Img1" runat="server" ImageUrl="/images/Submitn.png" OnClick="Img1_Click" /></td></tr><tr><td ><asp:DropDownList ID="ddl1" runat="server" AutoPostBack="true"                                        OnSelectedIndexChanged="ddl1_SelectedIndexChanged"></asp:DropDownList></td></tr></asp:View><asp:View ID="View2" runat="server"></asp:View></asp:MultiView></ContentTemplate></asp:UpdatePanel>

The button events and dropdown events are not getting fired. If I remove the update panel, then events are firing.

How to fix this?

Thanks