The script is quite simple, so I see no reasons to crash.
The issue is not simplicity. It's using CHDK to trick the camera into doing things it would not normally do and causing the Canon firmware to get confused. You can do that with a two line script if you try hard enough.
The original script goes from 0 to 127 zoom steps, but I modified it in order to go from 0 to 64 (half)
The SX100 has only 23 discrete zoom steps.
Here is the code:
Is that the entire script ? If so, you never release the "shoot_half" or the "shoot_full". That might be causing your problem.
You might also try starting the zoom process prior to initiating shooting? I don't know if that makes things better or worse but it's worth a shot.
Edit : there is
another thread about the same script that you may not have seen ?