How to use Session in Web Service web method in ASP.Net

sir i am following one of your links:

http://www.aspforums.net/Threads/184700/Assign-JavaScript-variable-value-to-ASPNet-Session-variable-using-JQuery-AJAX/

But this concept is not working in master page, i have kept the script in the master page and calling the function in the content page link button OnClientClick. Function gets called, but its not calling the webservice method, i have just replaced one line:

Kindly suggest, bit urgent.

url: "CS.aspx/SetSession", with url: 'WebService.asmx/SetSession',