AutocompleteExtender not work in master page

Question

Hi at all, i've a problem regarding the autocomplete extender in asp.net. It works fine in all page i do, but NOT in a master page. And i don't know why !!!

Here my code

<asp:TextBox runat="server" ID="txtSearch" Width="200px" CssClass="TextBoxClass"></asp:TextBox>
                                <cc1:AutoCompleteExtender ID="txtSearch_AutoCompleteExtender" runat="server" TargetControlID="txtSearch"
                                    CompletionInterval="0" CompletionListCssClass="autocomplete_completionListElement"
                                    CompletionListHighlightedItemCssClass="autocomplete_highlightedListItem" CompletionListItemCssClass="autocomplete_listItem"
                                    CompletionSetCount="10" EnableCaching="true" MinimumPrefixLength="2" ServiceMethod="GetCompletionListOggetti"
                                    ShowOnlyCurrentWordInCompletionListItem="true" UseContextKey="True">
                                </cc1:AutoCompleteExtender>

and the behind

<System.Web.Services.WebMethodAttribute(), System.Web.Script.Services.ScriptMethodAttribute()> _
Public Shared Function GetCompletionListOggetti(ByVal prefixText As String, ByVal count As Integer) As String()
    ' Insert code to return a string array here…
    Return AutoCompleteOggetti(prefixText)

End Function

The problem is that GetCompletionListOggetti is never called.

I repeat it works fine on content page.... !

Thanks in advance!