[WizenedEE]

I'm pretty sure the DIO ports on the C RIO are never left floating (at the very least not after they're initialized), so that doesn't make much sense. There's nothing in the datasheet about it, strangely enough, except that there's a 10K pullup already on it. Maybe that's not disconnected when it switches to output? That wouldn't make much sense though.

I'd say test continuity, and then go to voltage mode on your multimeter, and do one lead on ground and the other on the signal. If you get zero, put the first on 5V. If they're both zero, the pin in floating for whatever reason, if one is zero and the other is 5V, then it's something in the wiring/arduino.