I've always found it strange that the recommended best practice is always to upgrade your directory server first. On companies that started out with one server this tends to be their most critical. So, most companies, (mine included) upgrade some 'expendable' server first. Test their applications out there, test replication and clustering, etc. Also helps when you've RTFM but skipped a step, like ensuring your Java level was compatible with the newer Domino. Which I believe to be the #1 killer of which versions of IBM i support which versions of Domino.