Applies to computers running Windows.
The following information has been taken from this Ableton Knowledge Base article.
If the MIDI ports for your Novation device are red in Live's Preferences (orange in Live 9) they cannot be used, though they may still appear as available in the main Live window. This can happen if another application is using the device's port, or if Windows believes this is the case.
Please follow the below steps to fix this issue:
Turn off all the Track/Sync/Remote settings for the port. If the port is no longer highlighted red/orange, you can now turn the relevant Track/Sync/Remote settings back on. If this does not solve the issue, please move on to the next step.
Close all running applications that might be using the MIDI ports.
Disconnect all USB hardware (this excludes necessary hardware such as your mouse and keyboard).
Reinstall or update the drivers for your Novation product(s). Make sure to completely uninstall the old drivers first. You can download the latest driver for your product via the downloads page.
Reconnect your USB MIDI devices one after another and check to see if they are available in Live. If the device MIDI ports are still highlighted red/orange in the Live preferences, please try a different USB port and restart Live.
If you are unable to solve the issue by following the above steps, it may be necessary to follow the steps in this article.