<script language="JavaScript" type="text/javascript">
function MyPostbackClientSideFunction(sender, item){
//do a postback or whatever you want here
    __doPostBack();
}
</script>
<cc1:AdvancedAutoSuggestExtender SuggestOnEmptyField="true" TargetControlID="StateTextBox" ServiceUrl="~/Suggestions.asmx/StateSuggest" ID="StateAASE" SuggestionsDivId="suggestionsDiv" runat="server"  OnClientItemSelected="MyPostbackClientSideFunction" />