关于UpdatePanel有关问题

关于UpdatePanel问题,求助
因为现在工作上要求是要弹出对话框,无论怎么试都试不出来,都无法弹出对话框.后台代码的  TXTFOCQTY.Focus 和 TXTFOCQTY.Text = HIDFOCQTY.Value 是完全可以使用到的,我现在是想让他弹出对话框.求各位大神帮帮忙.小弟是一名小白.求助各位大神了

前端代码:

                    

<asp:UpdatePanel ID="UpFOCQTY" runat="server" UpdateMode="always"  ChildrenAsTriggers="true" >
                        <ContentTemplate>
                            <asp:TextBox ID="TXTFOCQTY" runat="server" Font-Names="Arial" Width="75px" Font-Size="10pt"
                                AutoPostBack="true" BorderStyle="None" MaxLength="11" Style="font-size: 10pt;
                                border-bottom: black 1pt solid; font-family: Arial; border-top-style: none; border-right-style: none;
                                border-left-style: none; height: 16px; text-align: right" Enabled="false" onKeypress="javascript:if (event.keyCode < 46 || (event.keyCode> 46 &amp;&amp; event.keyCode< 48) || event.keyCode> 57) event.returnValue = false;"></asp:TextBox>
                        </ContentTemplate>
                        <Triggers>
                            <asp:AsyncPostBackTrigger ControlID="TXTFOCQTY" EventName="TextChanged" />
                        </Triggers>

后台代码..

   
 Protected Sub TXTFOCQTY_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles TXTFOCQTY.TextChanged
        If CDbl(TXTFOCQTY.Text) > CDbl(HIDFOCQTY.Value) Then
            ScriptManager.RegisterStartupScript(UpFOCQTY, GetType(UpdatePanel), "alertok", "<script language='javascript'> alert('cao')</script> ", True)
            TXTFOCQTY.Text = HIDFOCQTY.Value
            TXTFOCQTY.Focus()
        End If
        If CDbl(TXTFOCQTY.Text) < 0 Then
            Page.RegisterStartupScript("ZXM2", "<script language='javascript'> alert('" & GetCap("NUMFORMATERR") & "')</script>")
            TXTFOCQTY.Text = HIDFOCQTY.Value
            TXTFOCQTY.Focus()
        End If

VB,NET
------解决思路----------------------
Page.RegisterStartupScript这个函数,顾名思义,它就是输出Script脚本的,当然就会自动给你外面套上Script标签