I encountered the same problem here, using gsoap 2.7.6e for building the client app and the currenct cvs scheckout for JBoss 4.0.4.CR2.
Most elements in the wsdl file are marked as nillable=true. The wsdl and the mapping file is generated with wscompile 1.6.
The c++ variables are not set (==NULL), so the soap mesage doesn't include the element.
The validation of the message in org.jboss.xb.* gives an error/excpetion that the element was not found in the xml fragment.
Using JBoss 4.0.4.CR1 with org.jboss.axis.* the webservice communication worked perfect.
My scenario is the same. The only diffrence being that I started with the WSDL and used WSCompile 1.6 to generate the stub code and jaxrpc_mapping file