When an array of objects is passed as a parameter webservices appears to check the first member and selects the correct subclass for instantiation. However, if a subsequent member is a different subclass an error results as it attempts to marshal into the same subclass. It then complains that there is a field that is not valid in that position. Apparently, it only checks once when processing a object array that is filled with multiple subclasses. There was a similar problem in pojo cache during replication last year and they were able to fix it over night. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4074627#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...