autocomplete in gridview not working

using <ajaxToolkit:AutoCompleteExtender to fill a textbox with data from table

i have written the AutoComplete.asmx, though i dont get any errors , the textbox is not getting autocomplete

i have put a breakpoint in asmx page but the file is not called

my html is

<ItemTemplate><asp:TextBox ID="txtName" runat="server" AutoPostBack="true" Width="200px" Height="15px" Text="0" 
                                               Enabled="true" Style="text-align: right" /><ajaxToolkit:AutoCompleteExtender
                                 runat="server"
                                 ID="autoComplete1"
                                 TargetControlID="txtName"
                                 ServicePath="AutoComplete.asmx"
                                 ServiceMethod="GetCompletionList"
                                 MinimumPrefixLength="1"
                                 CompletionInterval="10"
                                 EnableCaching="true"
                                 CompletionSetCount="12" /></ItemTemplate>