passing objects to web service

hello, I have a problem with passing a complex object to a web service. I am converting the object (into the required fields of the web service "object") before passing it to the web service. Once reaching the web service itself, all data that is passed is retained EXCEPT for the ID which is lost. The ID is not even converted back to default values (which is -1). It is simply 0. I'm not sure if I'm making any sense here, but has anyone heard of this before? Thanks