Reactor: rope and collisions

I'm having trouble getting my rope objects to "reactor" to collisions.
It's probably pilot error; my first time trying to use reactor for a real
project.
I have several ropes-- initially straight-- that have end vertices constrained
to rigid (unyielding) bodies. The rigid bodies are animated. The ropes do remain
constrained, and follow, stretch, wobble, and in general produce interesting
motion, but they pass through each other and the rigid bodies. 
Am i missing something basic? (probably...)

thanks,