Kwill The zone crashes occurring in the x2 Tower of Frozen Shadow instances involving boss Tserrina have been identified by the development team, but cannot be immediately fixed, says Gninja:
We have found the crash issue with Tserrina and it should be getting cleared up within a patch or two. For now if you do not cure the curses it should not crash.
Looks like Tserrina found a way to make her curses stick!