Web Service Prompts for Username/Password

Hi All,
I am trying to include a call to a web service on an asp.net web page.  The problem is i added a reference to the service so i could access it in javascript and now each time the page loads it prompts for a username and password for the server.  This is what I added to my page:
<asp:ScriptManager ID="ScriptManager1" runat="server">
            <Services>
                <asp:ServiceReference Path="WebService.asmx"></asp:ServiceReference>
            </Services>
        </asp:ScriptManager>
Can anyone let me know why it is suddenly prompting and how to prevent this?

...