I think I got it, Jadefalcon would you mind being my test subject#GP-02 ?
for users: put media03.bm with media01.bm in your Planet Alcatraz directory.
For devs I'm not quite sure about the REAL cause of the problem, but apparently deleting "user_control off' at the beginning of sullen_exploring.ers keeps the game going. My guess is that there is something else wrong before (bug in another script or buffer overflow, I don't know...).
EDIT:
1-thanks BFG5000 for confirming it works
2-for those who don't/don't want to/can't have a 1C account, you can find the fix here:
http://www.megaupload.com/?d=XXB7R8DO