Can't record! Help!

[earthboundaudio]

I had to cancel a session today b/c Tracktion doesn't seem to want to record on one of my edits and I can't really figure out why. The record function works fine on other songs I'm working on but it just won't work with my current edit. I hold down the record button and hit the play button on my Mackie Control and a little bubble pops up that says "autosaving", then song just starts playing but not recording. Very frustrating... any ideas?