<asp:TextBox ID="txtName" runat="server" Height="18px" Width="366px" 

            AutoPostBack="True" ></asp:TextBox>

        

<ajaxToolkit:AutoCompleteExtender

   runat="server" ID="autoComplete1"  TargetControlID="txtName"

ServicePath="WebService1.asmx" ServiceMethod="GetCompletionList"

 MinimumPrefixLength="1" />

它不是为我工作......
我已经试过.. {C1的}