i have created a form on which drop some controls and binded these controls at run time on page load event and these controls puted in update panel (Ajax)  on first dropdownlist chage event i have register javascript to show alert but unfortunetly it is not showing ,if i removing the update panel then it is working can any body help me please.
<form id="form1" runat="server">
    <div>
    <asp:ScriptManager runat="server"></asp:ScriptManager>
        <asp:UpdatePanel runat="server">
            <ContentTemplate>
                Accounts<br />
                <asp:DropDownList ID="ddlaccountnumber" AutoPostBack="true" OnSelectedIndexChanged="ddlaccountnumber_SelectedIndexChanged" runat="server"></asp:DropDownList><br />
                Currency<br />
                <asp:DropDownList ID="ddlcurrency" AutoPostBack="true" OnSelectedIndexChanged="ddlcurrency_SelectedIndexChanged" runat="server"></asp:DropDownList><br />
                    Amount <br />
                <asp:TextBox runat="server" ID="txtAmount"></asp:TextBox>
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
    </form>
 public partial class ABC : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                BindDDlAccount();
                BindCurrecy();
            }
        }
        protected void BindDDlAccount()
        {
            try {
                List<ListItem> items = new List<ListItem>() 
                {
                 new ListItem{ Text="12346790", Value="423423432"},
                 new ListItem{ Text="123455", Value="34356565"},
                 new ListItem{ Text="0908977867", Value="342224443"},
                 new ListItem{ Text="3425466768767", Value="6756455498797"},
                 new ListItem{ Text="435345657867", Value="3453456787987"},
                 new ListItem{ Text="345657787", Value="455467896"},
                 new ListItem{ Text="34564567678", Value="454678798797"},
                };
                ddlaccountnumber.DataSource = items;
                ddlaccountnumber.DataBind();
            }
            catch (Exception ex_) { }
        }
        protected void BindCurrecy()
        {
            try {
                List<ListItem> imtes = new List<ListItem>() 
                {
                    new ListItem {Value="PKR", Text="PKR"},
                    new ListItem {Value="USD", Text="USD"},
                    new ListItem {Value="INR", Text="INR"},
                    new ListItem {Value="OMR", Text="OMR"}
                };
                ddlcurrency.DataSource = imtes;
                ddlcurrency.DataBind();
            }
            catch (Exception ex) { }
        }
        protected void ddlaccountnumber_SelectedIndexChanged(object sender, EventArgs e)
        {
            string script = "<script>alert('cliked');</script>";
            Page.ClientScript.RegisterStartupScript(this.GetType(), "NAMe", script);
        }
        protected void ddlcurrency_SelectedIndexChanged(object sender, EventArgs e)
        {
        }
    }