suddenly bounce to track doesn't work using outboard sound module

I have Sonar X1d, M-Audio OMNI I/O DAC, and Delta 44 soundcard, and I frequently bounce to track this way:
1. Create a MIDI track
2. Send the output thru a Soundblaster midi out port to a Roland Rack mounted sound module
3. Send the Audio outs from the roland module to the input of the OMNI I/O, channels 3/4
4. Create an audio track, and set the audio in as from channels 3/4.
5. Record
 
This has worked perfectly for years, and I'm quite happy with it.
However, last night, after creating about 20 audio tracks and sending them to a bus, I forgot to bounce one
additional track, but suddenly it just won't work.
 
(From Step 4, the audio track doesn't respond, and there's no activity in the record meter.)
 
I checked all my settings from another project, and they work fine in another project, but suddenly not in
this one any more!
 
So I'm wondering if there's an anomaly I'm unaware of. For example, I just upgraded from 1xc to 1xd. Did this
introduce any bounce problems?
 
Or, does adding busses interfere with bouncing? Anything ring a bell?