The error message says the server has failed to properly handle the request.
It doubt if this is a result of the anyType data type you use in the response data structure, because error code 500 implies a problem in an earlier stage (before even trying to generate the response).
Are you sure the service you try to use accepts the inputs you have sent ("Text" for some parameters and nothing else)?
I would try to find somewhere a valid request that is properly served by the service and try to send the same input parameters.
For best results, use the Firefox browser..