To be able to record onto or play back an audio track, each track in your DP/AudioDesk project must have a voice assigned to it.

The easiest way to do this is to assign all of your tracks' voices to "Automatic", then have enough mono and stereo voices to cover them all. Voices are allocated under Setup > Configure Audio System > Configure Studio Settings.

However, you can also manually assign voices to each track. You can use the same voice for two different tracks, but if they both have audio at the same time only one track (the one higher up in the tracks list) will be heard. Voice-sharing between multiple tracks is best for things like the same instrument in two different parts of the sequence, such as the regular chorus and an alternate chorus, or an intro and outro.

If you can't record-enable a track, it may not have a voice assigned to it, or if you're using "Automatic", you may not have enough voices overall.

Also, the voice may have been dynamically unassigned if you have the "Mute Frees System Resources" option enabled under Setup Menu > Automation Setup.When you check this option in Automation Setup, muting a track causes the voice to become disabled (which will take away the ability to record-enable it). Once this "Mute Frees System Resources" option is unchecked, the voice will automatically be reassigned to the track and the record-enable button will reappear.

Finally, if the MOTU Auduio System (MAS) has been disabled, all of the voices are de-activated. Choose Setup > Audio System > MOTU Audio System to turn MAS back on.