segfault on contact

[Blue Prawn]

Hi,
I'm new to Chipmunk, I've tryed make a little script that reads the physics description from an XML file, and I've tryed to reproduce a very simple case with a circle above a ground static segment. First I've made this case with static code, it works right, then I've tryed to convert it in XML, and then a segfault occures when the circle collides the segment.

I guess there is an error in my XML to Chipmunk system.
Which error in the Chipmunk instructions could cause the demo to segfault when a contact occures?

(before a contact occures, all reacts as expected)

thanks in advance