Hi Anil,

You're missing the node-less library. The fixes:

sudo apt-get install node-clean-css 
sudo apt-get install node-less

This will install both the node-less JS library and the CSS rendering which Odoo 9 needs.

Yenthe

This error shows because of two reasons

1. You don't install required packages and plug-ins on your ubuntu system or

2. Install packages and plug-ins are outdated

To overcome this problem try this commands on your ubuntu terminal

• sudo apt-get install curl

• curl -sL https://deb.nodesource.com/setup_0.10 | sudo bash -

• sudo apt-get install -y nodejs

• sudo npm install -g npm (to update npm)

• sudo npm install -g less less-plugin-clean-css

Answer by Gajanan Kathar was useful but need to set npm registry before update, i.e. execute following command just before bullet point 4.

npm config set registry http://registry.npmjs.org/ 

Sure you have to install some package like this: 

sudo apt-get install node-clean-css

sudo apt-get install node-less

But, according to this comment in a bug report, you have to install website_blog module too: https://github.com/odoo/odoo/issues/8676#issuecomment-142604714

It works for me.