I struggled with you same issue for about 3 hours. As of
Compass 1.0.alpha19, the requirement is for the rvm version 1.9.3.
There are several uncollected posts, however what worked for me was the following:
sudo gem uninstall sass
sudo gem uninstall compass
rvm install ruby-1.9.3-p448
sudo gem install sass --pre
sudo gem install compass --pre
and that did it. Hope it works for you as well!