Suspend and hibernate don't work

When I select to suspend or hibernate my computer with Synapse, nothing happens (restart, shut down, and log out work just fine though). The entries appear, I hit enter, and then nothing at all happens. I'm using Ubuntu 11.10 and Synapse 0.2.8.1. If I go to the session menu indicator on the top right, I can select to suspend and hibernate my computer - and doing that works just fine. Is there something I'm missing? Thanks!