ASP.NET MVC AJAX Sys是未定义的错误

I am getting a "Microsoft JScript runtime error: 'Sys' is undefined" error on one of my pages in an MVC application when I attempt an AJAX call. The AJAX call is made from a partial view which is embedded in more than one page. It works fine on all of the pages except one. I have read posts pointing to the web.config file settings and .axd mappings as possible solutions, but the application is configured correctly in the web.config, and the .axd mappings are also correct in IIS. Plus it works fine on all of the pages that use this partial view except one. It is acting like the AJAX libraries are not loading for this one page. I am getting a "Microsoft JScript runtime error