I've got the same problem. After upgrading from v1.1.0 to 1.1.11 and then to v.1.1.12 in my Magento CE 1.4.2.0.

Nothing helps. At installing I've disabled output, disabled module itself, deactivated cache. After installing, I Logged in / Out, remove Cache files, activate all stuff ... nothing works ..

Any Idea?

P.S. I follow this steps: http://ebizmarts.com/forums/posts/view_reply/6434