Cannot enable track for recording

Hi everyone,

I'm trying to record a simple voiceover in Premiere Pro CS6.0.0, build 319 for Mac. Premiere recognizes my USB headset, but I can't select the "Enable Track for Recording" button (icon: a sans-serif capital letter R) in the Audio Mixer. It's not disabled/grayed out, but when I click it, nothing happens. I've tried this with and without the red "Record" button (bottom of audio mixer) selected. There's nothing on the track I want to record to. I have tried this with two different microphones.

I'm on Mac OS X 10.8.2, standard (non-admin) account. Everything else works fine. What gives?

Thanks!