Hello Wizardz, 

Please install node-less using below command

sudo apt-get update && apt-get install node-less

Hope it will helps.

Hello Jignesh Mehta, 

I tested it with this:

1) sudo apt-get update

2) sudo apt-get install nodejs

3) sudo npm install -g less-plugin-clean-css

4) sudo npm install -g less

But the same error is showing up. I have created a new database to test this all the web_ modules . But in Odoo9 nightly build the web modules show me every time the "LESS" errors.

1. Check the official documentation about installing dependencies of Odoo 9.0 and don't forget the symlink (Ubuntu 14.04 only)

https://www.odoo.com/documentation/9.0/setup/install.html     

2. If it does not help, check this:https://www.odoo.com/forum/help-1/question/ubuntu-server-14-04-howto-install-nodejs-npm-and-less-82575        

3. website_sign is an enterprise module. If you are an enterprise customer, you should get help from Odoo.

For you less try;

sudo apt-get install nodejs

sudo apt-get install npm

sudo npm install -g less

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

sudo ln -s /usr/local/bin/lessc /usr/bin/lessc

sudo ln -s /usr/bin/nodejs /usr/bin/node

However it might be a good idea to follow this example to the letter and you should be fine. I recommend a complete remove of what you have installed then reinstall. Link for instructions see bottom

Remove all

sudo apt-get --purge remove odoo

#not ideal but.. works.

sudo find / -iname 'odoo' -print -exec rm -r {} \;

# removal of PostgreSQL

sudo apt-get --purge remove postgresql\*

sudo rm -r /etc/postgresql

sudo rm -r /etc/postgresql-common*

sudo rm -r /var/lib/postgresql

sudo rm -rf /etc/apt/sources.list.d/postgresql.list

sudo userdel -r postgres

sudo groupdel postgres

sudo find / -iname 'postgresql' -print -exec rm -r {} \;

# if you see dependency problem it is most likely you have a problem that while install PostgreSQL you did this multiple times

# and therefor left some of those packages, you will need to remove them 1 by 1 before installing again!

# I  suggest the following for installing PostgreSQL

sudo apt-get install python-software-properties -y

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add - 

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main" >> /etc/apt/sources.list.d/postgresql.list'

sudo apt-get update && sudo apt-get install postgresql-9.3 pgadmin3 -y

Link for instructions installing v9 on trusty:

https://www.getopenerp.com/install-odoo-9-on-ubuntu/

I know that on ubuntu wily 15.10 ( you can use the deb file, and it will install without a problem) but some features might not work in version Odoo v9. For me I made a small bash shell script to install Odoo v8 on 15.10, do not think it will work for you on 14.x