Autocomplete with multiple value in Textbox ?

I am trying to implement autocomplete option with textbox with multiple values with comma separated but i am getting error in message box (alert).
I am using this article http://www.aspdotnet-suresh.com/2012/07/jquery-autocomplete-textbox-with.html as base but instead of list<string>, i am returning List<AuthorDetail> .
What is wrong in code?
<asp:Content ID="content1" runat="server" ContentPlaceHolderID="AdminHead"> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.1/jquery-ui.min.js"></script> <script type="text/javascript"> $(document).ready(funct ...