anonymous wrote : Nops, There is only one jar file common-collections.jar in ....default\lib\. I meant, do you have multiple copies of the same jar file on the server? anonymous wrote : | And it is there in build path of both EJB as well as Web app. | You mean that the deployed ejb jar and the web app each have a copy of the common-collections.jar file? If yes, then that might be the cause of the LinkageError. The OrderedMap might be loaded by 2 different classloader (one from the ejb and the other from the web app). Are the ejb jar and the web app part of the same application? If yes, then you could deploy them as an ear file and have only one commons-collections.jar in the ear instead of at 2 places. Also, did you try the jmx-console method mentioned in the link that i posted earlier? That's going to tell you whether the OrderedMap is being loaded from 2 different commons-collections.jar file. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4065547#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...