无法使用jQuery从ASP.NET Web服务返回JSON对象

I am finding many "solutions" to this seemingly common problem, but alas, none seem to work for me - of course. I have some jQuery code that is trying to post to an ASP.NET 3.5 web service. The web service is supposed to return some json. I am getting 501 Internal Server errors with the code below, but according to the solutions found online, this is how it is supposed to be! The error function in the jquery code displays a parsererror. If I change how the data parameters are passed to the service (I am finding many "solutions" to this seemingly