Like we told you back then, the script wasn't perfect: it didn't enqueue folders recursively and also if some songs had some special characters, all the selected songs would fail to be added to the Rhythmbox play queue. But Seemanta, the developer of this plugin released a new version a few days ago which addresses these bugs.
To download and install the new, improved Nautilus plugin for Rhythmbox, simply paste this in a terminal:
sudo apt-get install python-nautilus
rm ~/.nautilus/python-extensions/add-to-rhythmbox.py #in case you installed the old version
wget http://seemanta.net/code/Nautilus_plugin/add-to-rhythmbox_V02.py
mkdir ~/.nautilus/python-extensions
mv add-to-rhythmbox_V02.py ~/.nautilus/python-extensions/
nautilus -q
The credits for "Add To Rhythmbox Play Queue" Nautilus plugin go to: Seemanta.net