I have .NET web service which supposed to return the result as JSON, but it returns it as XML? Here is my code.

 [WebMethod, ScriptMethod(ResponseFormat = ResponseFormat.Json)]
 public List<MyData> GetMyData(string dataFilter, string param)
 {
 if (dataFilter.ToLower() == "filterValue")
 return getData(param);
 return null;
 }
And here is 

 <system.web>
 <compilation debug="true" targetFramework="4.0"/>
 <httpRuntime/>
 <customErrors mode="Off"/>
 <webServices>
 <protocols>
 <add name="HttpGet"/>
 <add name="HttpPost"/>
 </protocols>
 </webServices>
 <pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID"/>
 </system.web>