[dominicperry]

You could try a device reset of the Carbon. From the manual:
Default Device Settings
If necessary, you can restore the default system settings (such as preamp gain, monitor gain, and so on).
To restore the default system settings for Pro Tools | Carbon:
1 Lower the volume on all output devices and mute your speakers.
2 Power off the unit.
3 Press and hold the Meter button while powering on the unit.
4 Hold the Meter button for 20 seconds while the device front panel is lights in the green start-up state.
5 After this, release the Meter button.
The device starts up with the default settings after the Meter button is released.

However I think the problem is with a preferences/config file in PT.

From a previous post (I think from an Avid rep.)
Another thing to try is to delete "Pro Tools_Carbon.pio" and "Last Used.pio" in the PT preference folder and re-launch Pro Tools. These are located in:
Macintosh HD/Users/<user name>/Library/Preferences/Avid/Pro Tools

You can quickly get there by clicking Finder > Go > Go to Folder...., then entering the following and clicking Go:
~/Library/Preferences/Avid/Pro Tools/

Looking in this folder I can see there is also a Pro Tools_Carbon Expanded.pio, which you would have if you are using Carbon Central (rather than Audio Midi Setup) and you'll have to delete that file too.

Dominic