Hi,
I am working on CascadingDropDownExtender in AJAX. When I run the sample, I am getting “[Method Error 500]” in the Dropdowns. I wrote a Web Service (carService.asmx) to get the values from the XML (carService.xml) into the Dropdowns. Even the Web Service is not invoking correctly. When I run the Web Service, an XML is generated with errors. Please help me with the solution. Thanks.
Start debugging your webservice. Looks like thats where the problem is. Have a look at this Microsoft article: http://support.microsoft.com/kb/311766
Bit late for a answer, but it could help somebody else.
I had a similar issue, but initially I was getting a "method error 415", then later a "method error 500". I would suggest checking your bindings for the webservice.
What I realized is that I accidental added the service as a Silverlight enabled service instead of a AJAX enabled service. I ended up redoing the service bindings in the web.config, which lead to the "method error 500". Obviously I modified the service bindings incorrectly and instead ended up recreating the service but as a AJAX enable service. Everything worked as expected afterwards.
P.S. I am using WCF services, but I am sure the same applies for normal webservices.