Cannot create page method "GetCompletionList"?

Hi,

I am using the link below to try and do an autocomplete textbox:

http://www.asp.net/ajaxlibrary/act_AutoComplete_Simple.ashx

When I try to add an autocompletepagemethod I get the error "Cannot create page method "GetCompletionList"? because no CodeBehind or Codefile was found.

I added the AutoComplete.aspx file from the tool kit to my project. Any ideas?

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></asp:ToolkitScriptManager><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><asp:AutoCompleteExtender ID="AutoCompleteExtender" runat="server"
        DelimiterCharacters="" Enabled="True" ServicePath="" TargetControlID="TextBox1"
        UseContextKey="True"></asp:AutoCompleteExtender>