Port Error when adding second MOXF VST track

My Yamaha MOXF8 keyboard is successfully recording and playing back from a Cubase track, but I am having trouble getting the MOXF voice I want on each track. Running Windows 8.1.

I have been adding instrument tracks on Cubase (AI 8) and assigning MOXF8 VST instruments. The first track synchs completely to the MOXF8 and the voice playback works OK. But the second track fails to synch to the MOXF8 when I add it’s instrument. I get a PORT ERROR. The playback of the second track fails to play back thru the keyboard.

I am able to define multiple instrument tracks with HALION VST instruments with successful playback of different voices on each of the Halion tracks.

I’d appreciate any help as to what is preventing me from getting a second MOXF VST track to work properly.