Make sure Noteworthy has something to use for playback.

Go to Tools/Options and select the Midi tab.

There should be two windows. On the left "Available Play Devices" and on the right "Devices used by Playback". (This is how it looks in v2.1 but v1.75 was pretty much the same IIRC.)

Make sure the window on the right has something in it. If there is nothing on the right hand window, click on one of the available play devices on the left and send it to the right hand window using the arrow between the two windows. Midi mapper will usually be fine unless you have something special you use.