cascade dropdownlist not working in update panel

Hi All,

I am using 2 cascading dropdownlist with a label to show a value (within a contentplaceholder i.e. using master page). All is working fine. On selecting ddlLocation it is binding ddlProjects and after selecting ddlProjects item it is showing related value in txtClient. ()

But when I tried to put those in a update panel to get rid of the whole page post back, then those don't work. After selecting one item in first dropdown list it doesn't refresh the second one.

Below is my aspx page.

<asp:UpdatePanel ID="Updatepanel1" runat="server"><ContentTemplate>                              <asp:DropDownList ID="ddlLocation" runat="server" Width="150px" DataTextField="Location" DataValueField="Location" OnSelectedIndexChanged="ddlLocation_SelectedIndexChanged" AppendDataBoundItems="True" AutoPostBack="True"><asp:ListItem>-Select</asp:ListItem></asp:DropDownList><asp:DropDownList ID="ddlProjects" runat="server" Width="150px" OnSelectedIndexChanged="ddlProjects_SelectedIndexChanged" AppendDataBoundItems="True" DataTextField="Project_Name" DataValueField="Project_Id"><asp:ListItem Value="0">-Select-</asp:ListItem></asp:DropDownList><asp:Label ID="txtClient" runat="server"></asp:Label></ContentTemplate>  </asp:UpdatePanel

Why it is not working.

Please suggest.