ASP.NET AJAX 1.0 by default only allows the HTTP POST verb
to be used when invoking web methods using JSON, which means you can't
inadvertently allow browsers to invoke methods via HTTP GET.
ASP.NET AJAX 1.0 requires a Content-Type header to be set to
"application/json" for both GET and POST invocations to AJAX web services. JSON requests that do not contain this header will be rejected by
an ASP.NET server. This means you cannot invoke an ASP.NET AJAX web
method via a <script src=""> include because browsers do not
allow append custom content-type headers when requesting a JavaScript file like
this.
Hope this helps,
Scott