As I said, I know nothing about the library you are using so I will not be able to help.
Have you tried to put a breakpoint in your code just before the try block and then step through the code? This should give you some information as to which statement is really throwing the exception.
Also, put the return value in an object variable and then somehow log the type of it, something like:
object response=envelope.bodyIn;
Log.d("MainActivity", response.getClass().toString());