What ORB are you using; you sure it donsn't run on Java5. Another option would be to switch to the JacORB implementation that comes with JBoss? AFAIK EJB3 requires Java5, so there is nothing you can do for this (you can ask in the ejb3 users forums just in case).
Thanks for the response.
We're using Orbacus which does work on 5 in later versions, but we're definatley stuck at an early version. We'd love to use Jacorb, make life much easier but theres a whole load on Orbacus.
Looks like we'll have to abandon EJB3 for now. :-(