thanks for the reply. At first, no I just switched in the new library, but when I saw the problem I copied in the entire resource directory.recompiled GWT and same problem. (refreshed cache in browser etc). But I agree it does look like that kind of problem. I've now realised its with all menus (e.g. button menus as well).
UPDATE - it must have been cached somewhere - perhaps on my server. It now works. Thanks for your time.