Hi
Doesn't it suck when someone just tells you it works for them and lets it go?! Sorry, I got lightheaded and realized I should probably eat something!
But I thought of something else. I don't think the name of the group type (Group Type) can have any characters other than letters or underscore in it (no spaces).
If that's not it, try calling group_type::new -group_type $object_type -supertype $supertype $pretty_name $pretty_plural
directly and see if it gives ya better error information.