In the MIDI tab of your synth (for example, the TripleOscillator), did you check "ACTIVE MIDI OUTPUT"?
If so, by clicking on the keyboard icon, did you select "Microsoft GS Wavetable Synth"?
If so, this is the reason for the problem.
If not, I just don't know.
To use a MIDI keyboard, check only "ENABLE MIDI INPUT", and select your MIDI device via the keyboard icon.