[Xignal]

The patch is supposed to help with the Kerah situation. Other possible solutions:

Save very frequently. Hide behind one of the pillars until Cet leaves. Fight Kerah (no spells) until she asks for holy water. When she turns back to normal make no movements with the mouse or keyboard until she disappears then quietly head upstairs - again saving often.

If you still can't make it through the encounter then you might e-mail me your zipped, saved game and I can try it on my system - just to get you past this spot.