Digital keyboard / Midi randomly stopped working when using virtual instruments

[kabster1985]

Hi.
Just recently I came back to work on a track of which I had recorded using virtual instruments, through my digital piano both a piano track (using XLN's Addictive Keys) and an orchestral string section (using VSL Epic Orchestra). Previous to this problem everything was working fine.
I would open an Instrument track, select a virtual instrument, arm the track and I would be able to play and record as normal.
I've spent many hours searching the internet for a fix but so far I've been unsuccessful.
What is confusing is it was working perfectly fine one day and then another day Pro Tools decided stop receiving a signal/MIDI from my digital piano.
If I run the virtual instruments I mentioned as stand alone programs separate of Pro Tools they work fine.

I am using a Zoom UAC 2 external sound card with a Yamaha p-45 digital piano. The Zoom UAC 2 is linked via a USB 3 cable and the Yamaha p-45 is USB 2.

What's baffling is I've used this setup and had little or no problems for a while now and the fact that the stand alone versions work perfectly does not really make much sense.

If anyone has any ideas to what is causing this problem and a fix I would be over the moon!

Thanks