I have found a workaround but it still doesn't give me the locking semantics that I would like. I have added a version number to my entity bean and added the @Version annotation. This means that the MDBs can read dirty data but can't write after using it; this stops the symptoms but doesn't fix the cause. Does anyone know how I can completely lock an Entity within a transaction? Regards Doug View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3959606#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...