If you are using ubuntu and having errors/warns of sass & lessc ,etc in your odoo webapp, Then you should try following for them:-

[Removing Hotch Potch]

$ sudo su     # Switch To Root Before Working ##
# rm -f /usr/bin/lessc /usr/bin/node
# apt remove node*
# cd /etc/apt/sources.list.d
# rm -f chris-lea-node_js-trusty.list *.save neurobin-ppa-trusty.list noobslab-apps-trusty.list 
# rm -f /var/cache/apt/archives/lock 
# apt-get clean

[Installing Required Deps]

# apt-get install python-pip python-dev libevent-dev gcc libxml2-dev libxslt-dev node-less libldap2-dev libssl-dev  build-essential zlib1g-dev libssl-dev libreadline6-dev libyaml-dev python-software-properties ruby -y

[Installing Compatible NodeJs & lessc]

# apt-add-repository ppa:chris-lea/node.js
# apt-get update
# apt-get install nodejs

# npm install -g npm
# npm install -g less less-plugin-clean-css
# npm install -g less
# npm install -g node-less

# rm -f /etc/apt/sources.list.d/*.save /etc/apt/sources.list.d/*.log

[Installing Ruby > 2.0 & Required Sass gems]

# cd /tmp
# wget http://cache.ruby-lang.org/pub/ruby/2.0/ruby-2.0.0-p481.tar.gz
# tar -xvzf ruby-2.0.0-p481.tar.gz
# cd ruby-2.0.0-p481/
# ./configure --prefix=/usr/local
# make
# make install
# ruby --version     # Should be greater than 2.0

# gem install sass
# gem install bootstrap-sass
# gem install compass

[Starting Your WebApp]

# cd <path to main source code>
# python openerp-server -c openerp-server.conf

Thanks!! n Have Nice Time !!