Call ASP.NET PageMethod/WebMethod with jQuery - returns whole page

Question

jQuery 1.3.2, ASP.NET 2.0. Making an AJAX call to a PageMethod (WebMethod) returns the full/whole page instead of just the response. A breakpoint on the page method shows

Answer 1

I encountered this problem again today for a different reason: I had misspelled "application" in

contentType: 'application/json'

And was getting a full-page response instead of a call to the WebMethod.