The reason was that group nodes tried to reconstruct sockets from the template lists, which are empty. Now the verification function checks if there are any sockets in the template lists, which are always empty for group nodes.
This branch adds mostly organizational improvements to the node system by renaming the node folders and files. A couple of internal features have been added too.
Detailed information can be found on the wiki page:
http://wiki.blender.org/index.php/User:Phonybone/Particles2010