p = hou.parm(parmPath).evalAsFloat()
Particularly the evalAsFloat function is what is breaking it. Has anyone had this problem before or does someone know some kind of work around? Smells like a bug to me.
EDIT: eval function only gives me trouble if it is trying to evaluate a parameter from the top level of the HDA. It works fine on nodes within the geometry network. I would still like to know if this was intentional or a bug.