Today I was trying to call a web service from Java Script using the Sys.Net.WebServiceProxy.invoke function but the following error was loading:
‘Sys’ is undefined
The problem was because the ajax was not being referenced in the website. The solution I found was to create a new website in Visual Studio 2005 and use the AJAX Control Toolkit Web Site Template. When I ran the code again, no error was loaded and everything worked fine!