Unfortunately, there is no way to fix this other than re-loading a save before you entered the castle and talked to Janus the first time. I tried awhile ago and posted in the old forum for someone else. I could swap files around to trigger the cut scene with the cat, but after restoring the original files (required so as not to break other quests) the next quest would not work. <img src="/ubbthreads/images/graemlins/disagree.gif" alt="" />
Hopefully the patch CDV is currently testing will detect and fix this bug.