A few things...
1. The script decompiled for me just fine.
2. Isn't Trask dead when you get to that area?
3. What exactly isn't working, and what is? I can see a few things that in my experience have a 50% chance of working, but if they're working then any advice wouldn't be helpful.
4. Why's it necessary to have an "if oStalker isn't valid"? If you're doing everything with the OnEnter script, he should never be valid, right?
5. "qg_pnd_1b_area" - is that a typo?