I've found the root cause of my case. Probably this help to others. My web method returns an object. One of it's fields was Timestamp. Once I changed it to Calendar (Soap compatible) Exception dissapeared. Exception trace contained absolutely no hints to that, though. I think this is something to work on : making a message more informative. Thanks again. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4104684#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...