Grunt need compass installed in system PATH Warning

The warning seems to say it all.

1. If you're on OS X or Linux you probably already have Ruby installed; test with ruby -v in your terminal. When you've confirmed you have Ruby installed, run gem update --system && gem install compass to install Compass and Sass.

2. If that doesn't help, then install the grunt-contrib-compass package with the instructions at https://github.com/gruntjs/grunt-contrib-compass

I struggled for hours with this same error message when running a gulp watch, and despite installing, reinstalling, rebooting, it would still show up.

Got it working by uninstalling all my packages :

sudo gem uninstall bundler bundle compass sass compass-core compass-import-once

And installing bundle only

sudo gem install bundle bundler

And then run the command that magically installed everything I needed :

$ bundle
Fetching gem metadata from https://rubygems.org/...........
Fetching version metadata from https://rubygems.org/..
Installing sass 3.4.9
Installing sassy-maps 0.4.0
Installing breakpoint 2.5.0
Installing hitimes 1.2.2
Installing timers 4.0.1
Installing celluloid 0.16.0
Using chunky_png 1.3.3
Using multi_json 1.10.1
Installing compass-core 1.0.1
Using compass-import-once 1.0.5
Using rb-fsevent 0.9.4
Using ffi 1.9.6
Using rb-inotify 0.9.5
Installing compass 1.0.1
Installing json 1.8.1
Installing listen 2.8.3
Installing thor 0.19.1
Installing fontcustom 1.3.7
Installing modular-scale 2.0.5
Installing normalize-scss 3.0.2
Installing sass-css-importer 1.0.0.beta.0
Installing sassy-buttons 0.2.6
Installing susy 2.1.3
Using bundler 1.8.0
Bundle complete! 9 Gemfile dependencies, 24 gems now installed.
Use `bundle show [gemname]` to see where a bundled gem is installed.
Post-install message from compass:
    Compass is charityware. If you love it, please donate on our behalf at http://umdf.org/compass Thanks!
Post-install message from fontcustom:
>> Thanks for installing Font Custom! Please ensure that fontforge is installed before compiling any icons. Visit <http://fontcustom.com> for instructions.

Now, don't ask me why, but it all works :-)

Hope that can help anybody out there, I really struggled on this one ...