Android : json reading error in robospice

Logcat error

07-29 12:57:57.920: E//DefaultRequestRunner.java:153(3697): 12:57:57.931 Thread-8869 An exception occurred during request network execution :Could not read JSON: Can not deserialize instance of java.lang.String out of START_OBJECT token

and this is my code in using robospice

RestTemplate restTemplate = new RestTemplate();


 // Add the Jackson and String message converters
            restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            restTemplate.getMessageConverters().add(new StringHttpMessageConverter());






 // Make the HTTP POST request, marshaling the request to JSON, and the response to a 
        String response = restTemplate.postForObject(url, message, String.class);


        return response;

Note: this same code is working fine some of the json output, some different kind of json, I'm getting this error, I tried to find out the json structure where exactly but what I feel both are same, so I get confused, at the same time I shout the reason of this error