I had this error for a very long time when trying to use extensions in Inkscape 0.46 for Mac OS X:
“The fantastic lxml wrapper for libxml2 is required by inkex.py and therefore this extension”
After many hours of trying to find a solution I got it to work. This is what I did:
sudo easy_install lxml
cd /Applications/Inkscape.app/Contents/Resources/lib
mv [...]