There is a naming conflict with the node package (Amateur Packet Radio Node Program), and the nodejs binary has been renamed from node to nodejs. You'll need to symlink /usr/bin/node to /usr/bin/nodejs or you could uninstall the Amateur Packet Radio Node Program to avoid that conflict.
solution: delete the node package:
apt-get remove node
then:
cd /usr/bin
ln -s nodejs node
then just run: in the etherpad-lite directory
bin/run.sh
and it works ... =)