Hmm, according to the Common Collections javadoc, org.apache.commons.collections.map.LinkedMap implements org.apache.commons.collections.OrderedMap. Maybe your copies of common-collections.jar on the server and client sides are incompatible. Note that common-collections.jar comes with the JBoss Application Server in the server/< configuration >/lib directory (where < configuration > is "default" or "all" or whatever). Maybe you have a different version of common-collections.jar on your client side classpath ??? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4072828#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...