Hi,
May be it is not able to find the information that is sent in the request. Usaually, response contains code and the reason when the request did not meet the criteria which you are seeing in your response. There can be response code and message for succesfull response as well based on the service implementation.
You may try with correct data in the request and it should give you correct details, other wise it could be an issue in the service, please talk to your service proivder or concerned person who hosted the service.
Hope this helps.
Regards,
Rao.