The javax.xml.rpc.encoding.XMLType class in JBossWS incorrectly defines the QName constants. For example SOAP_STRING is defined as:
public static final QName SOAP_STRING = QName.valueOf("

string");
It must be defined as
public static final QName SOAP_STRING = QName.valueOf("

string");
or
public static final QName SOAP_STRING = new QName("http://schemas.xmlsoap.org/soap/encoding/", "string");

Generally, the namespace URI must be http://schemas.xmlsoap.org/soap/encoding/ for the SOAP_xxx constants and http://www.w3.org/2001/XMLSchema for the XSD_xxx constants.