Populate jQuery autocomplete for TextBox inside GridView control in ASP.Net

Hi,

I am trying to use j-query autocomplete but i am getting this error: "The name 'txt_UID' does not exist in the current context"  I am using the same code that Mudassar Khan posted on his website but the example i was following uses a text-box that was outside of the gridview.  But my textbox is inside the gridview.  How can i make the autocomplete to work a text-box that is inside gridview?  please please help.  thank you so much.  here is my code:

-- here is my javascript
<script type="text/javascript">
        $(document).ready(function () {
            $("#<%=txt_UID.ClientID %>").autocomplete({
                source: function (request, response) {
                    $.ajax({
                        url: '<%=ResolveUrl("~/Service.asmx/GetUserNames") %>',
                        data: "{ 'prefix': '" + request.term + "'}",
                        dataType: "json",
                        type: "POST",
                        contentType: "application/json; charset=utf-8",
                        success: function (data) {
                            response($.map(data.d, function (item) {
                                return {
                                    label: item.split('-')[0],
                                    val: item.split('-')[1]
                                }
                            }))
                        },
                        error: function (response) {
                            alert(response.responseText);
                        },
                        failure: function (response) {
                            alert(response.responseText);
                        }
                    });
                },
                select: function (e, i) {
                    $("#<%=hfUserId.ClientID %>").val(i.item.val);
                },
                minLength: 1
            });

        }); 
</script>

-- and here is my gridview:
     <asp:GridView ID="GridView1" runat="server" Width="870px"
                    AutoGenerateColumns="False" Font-Names="Arial" Font-Size="11pt" AlternatingRowStyle-BackColor="#C2D69B"
                    HeaderStyle-BackColor="green" ShowFooter="True" 
                      
                    CellPadding="4" BackColor="White" BorderColor="#336666" 
                    BorderStyle="Double" BorderWidth="3px"
                    DataKeyNames="TSK_ID">
                    <AlternatingRowStyle BackColor="#C2D69B" />
                    <Columns>

                       <asp:TemplateField ItemStyle-Width="150px" HeaderText="User Name">
                            <ItemTemplate>  
                                <asp:TextBox ID="txt_UID" runat="server" Text='<%# Eval("UID")%>'
                                     Width="230px" BackColor="LightGoldenrodYellow"></asp:TextBox>
                            </ItemTemplate>
                            <ItemStyle Width="150px" />
                        </asp:TemplateField>
                    
                        <asp:CommandField ShowEditButton="false" >
                        <ItemStyle Font-Size="Smaller" ForeColor="#FF3300" />
                        </asp:CommandField>
                    </Columns>
                    <FooterStyle BackColor="White" ForeColor="#333333" />
                    <HeaderStyle BackColor="#336666" Font-Bold="True" ForeColor="White" 
                        HorizontalAlign="Left" />

                </asp:GridView>