Hello Angelo,
When dealing with Webservices, its the server you are trying to reach (most of the time), that will return an answer with an error code if the error happens.
If the error is "internal" to the service, you need to look for the documentation of the service.
If it's a more "server" error, it will also return the error in the answer, but usually are the codes like 404, etc, that are http errors, you can find the list on google ;)
You can deal with the answer before the platform throws an exception (a generic one).