So I have a mac running 10.11.4 (El Capitan).
I followed this tutorial: http://kiattipong.blogspot.com/2015/05/setup-odoo-development-on-os-x-with.html?showComment=1
I seems it was a node/npm issue. I had installed the node.js package which brings npm. I googled and found that there were issues if npm was installed without first removing an older version of it?
https://gist.github.com/DanHerbert/9520689
Somewhere I found this command:
sudo rm -rf /usr/local/lib/node_modules/npm
I removed npm and then reinstalled but this time I installed node from brew:
brew install node
Then I was able to follow the section here on lessc error and Odoo seems to be running fine:
http://jingigirl.blogspot.com/2015/10/install-odoo-90-on-mac.html
In this post it states that one must instal less and then less-plugin-clean-css and finally upgrade node which in my case wasnt necessary because I already had node 5.10.0.
What led me to the issue was that even after installing the node.js from nodejs.org, when I entered node -v I received an error node not installed!