I was meddling with settings (on my RME Babyface and within Nuendo) and all of a sudden I cannot trigger any MIDI notes in Nuendo.
I use a Korg MicroKey (via USB) to play notes. I am able to trigger standalone synths no problem.
I am able to play MIDI tracks from old Nuendo project files. These play the notes on my virtual synths. I just cannot play the synths or record MIDI notes with my MicroKey as I used to. Oddly there is in fact MIDI activity shown when I play keys on my Kor MicroKey.