Late to the party, and the OP may have already tried and found their answer, but since the non-disc wheel isn't dished the way a disc wheel would be, the spokes may interfere with your disc brake caliper. That was my experience recently (not to ride, just wanted to see if a particular tire would fit and I didn't feel like removing it from one wheel and mounting it on the other. But that laziness paid off in an experience I can share. ).

Mike