On JBM 1.4, the JCA adapter is part of the application server. So MDBs are not really part of JBoss Messaging 1.4. (Differently on JBM 2, as we are writing our own JCA adapter). I suggest you ask this on the JCA Forum (http://www.jboss.org/index.html?module=bb&op=viewforum&f=136) But anyway, you could also make the method onMessage of your MDB synchronized. So you would solve the multi-thread issue you have at your native lib. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4247339#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...