Hi Jon, Carbon's collision is very robust and so let's try and figure out what's up with your scene.
First I would suggest you check out the Carbon Avatar example. You can find it in the Carbon docs installed locally, or here on the web
carbon0220m.numerion-software.com/downloads.html
Check out the cloth, collider and simulation settings and see if that helps you figure out what's going wrong with your scene.
To properly see what is happening with collision you also need to hide the geos so that you are just using Carbon Physics Draw to draw your objects.
You'll see in the avatar example that the geo rendering is zbuffer fighting with the physics rendering - so just hide the geos by selecting each in the outliner and hitting "h"
If after checking out the avatar example, you are still having problems, then best to send us the .mb if you can, email to support @ numerion-software.com Or at least maybe share some screenshots so we can see what problem you are having.
Cheers,
Mike