Have you applied the 1.2 -> 1.2.1 patch? Are you indeed trying to run 1.2.1, or did you install 1.1? I don't insult your Intelligence by asking, it just seems odd to me, that it's not working...
I've never run into this problem, so I don't really know the solution... Try uninstalling ESF, reinstalling, and then applying the patch. That's the only advice I can offer.