It seems that my GIMP plug-in hacking has caused the print plug-in (which is mainly developed at sourceforge) to be totally incompatible with GIMP 1.0 and even all GIMP versions before 1.1.17
But it also seems that this problem seems to be solved soon, as it pointed both sides to the fact that we need some sort of core/ui separation for this plug-in. Doing this will also help turning the plug-in into a standalone application which can be plugged into a variety of applications (like sketch).
Synergy at work?
Anyway, if you've seen the output of the Gimp-Print plug-in, you'll love to have it pluggable into other apps. Believe me :-)