I have Music Creator 6 (MC) on my laptop (LAP), a Ketron (KET) SD-2 module as my instrument source, a Roland (ROL) A-49 keyboard controller for MIDI signals, and a Behringer (BEH) USB mixer. I can’t make this tangle of cables and contraptions function as a workstation. For starters, I don’t grasp the line of communication. I would suppose that ROL sends, say, and F# message to an MC MIDI track onto which it is recorded; MC sends that message to KET which is set to trumpet; that audio signal is sent to BEH via the RCA cables; and BEH lets me hear the trumpet track. When I’m happy with all the tracks, the mix of BEH , being connected USB to LAP is recorded as an audio track in MC.
 
Please correct me if this is wrong. Also advise as to what MIDI devices IN/OUTS and instruments are to be selected in the Preferences windows. 

Welcome to the forum.
What model is the Behringer? I'm assuming it is also an audio interface. If so, make sure you have the latest drivers for the device and your operating system.
Get the latest drivers for the Roland, too.
In Preferences, what is listed now for your MIDI In/Out?
 
Music Creator has it's own forum, so don't be surprised if this is moved over there.

geowonders
 
I have Music Creator 6 (MC) on my laptop (LAP), a Ketron (KET) SD-2 module as my instrument source, a Roland (ROL) A-49 keyboard controller for MIDI signals, and a Behringer (BEH) USB mixer. I can’t make this tangle of cables and contraptions function as a workstation. For starters, I don’t grasp the line of communication. I would suppose that ROL sends, say, and F# message to an MC MIDI track onto which it is recorded; MC sends that message to KET which is set to trumpet; that audio signal is sent to BEH via the RCA cables; and BEH lets me hear the trumpet track. When I’m happy with all the tracks, the mix of BEH , being connected USB to LAP is recorded as an audio track in MC.
 
Please correct me if this is wrong. Also advise as to what MIDI devices IN/OUTS and instruments are to be selected in the Preferences windows. 

no, that's a poor path connection.
 
connect the Roland Keyboard up with a MIDI cable from the Roland MIDI OUT to the Ketron MIDI IN.  then connect AUDIO cables from the Ketron AUDIO OUTPUT (R & L) to a stereo INPUT of the Behringer.  I would recommend using 1/4" cables for this instead of RCA and going to one of the main inputs instead of the RCA inputs on the berhinger.
 
then you have your behringer connected to the laptop using USB.  this sends the audio from the Ketron into MC.  at this point, you set up an AUDIO track with inputs of the BEHRINGER stereo selection and you will then record the output of the Ketron onto an audio track in MC.

How would that record a MIDI track in MC? Were I to connect the Roland's USB port to my laptop as well as to my Ketron via MIDI cable, would it record a MIDI track? If so, then I can see that your path might work for me since I do extensive MIDI editing. Meantime, Gary, the apparent creator of  believes my linkage is correct. He says that when we find time to talk on the phone, he'll guide me on the settings. If so, I'll let you know.

Also, where do I find Ketron instrument definitions? They are not included on Cakewalk's User-Created Definitions list and though Gary sent me this link:  when I try to import the download, Cakewalk says: No items match your search. 

I see that my links were not included above. Gary is with keyboardforums. I don't know how to direct you to the Ketron definitions he sent.
 

if you want to record the MIDI, then you will have to connect the keyboard to the computer, of course.
Does your Ketron have MIDI thru?

Yes, the Ketron SD-2 has MIDI thru. Today, with the connections I described, I finally got the controller to play but the latency was awful and I found no way to correct it through buffer settings. Maybe going from the Roland controller to the Ketron module will correct that. Unfortunately I've got to get a MIDI cable - I gave all mine to Goodwill last year. And what driver mode is right? ASIO? MME?

ASIO is usually best for recording if they're available.
Have you tried updating the drivers for the Behringer and the Roland?

sorry, I didn't realize you intended to record the MIDI first.
 
if that's the case, then what I would do in order to eliminate latency is this:
 
connect the Roland up to the computer using USB.  set up a MIDI track in MC to record that roland MIDI input
connect the Roland's MIDI output port up to the Ketron's MIDI input.
connect the Ketron's audio output to the behringer (again, I do not recommend using the RCA ports for this - use 1/4" connections to one of the main stereo inputs)
send the output of the behringer to the speakers.
there is no need to connect the behringers' USB connection to the computer at this time, nor do you need to set up an audio track in MC to record anything at this time.  currently you're just going to record the MIDI, but you'll HEAR the ketron output directly with no latency as you hit record and begin playing the roland.
 
after you've created the MIDI track in MC, you may edit it as you desire.
 
then you need to connect the Ketron MIDI OUTPUT to the computer.  this might require additional hardware you don't currently have.  you'll need a MIDI to USB cable to do this.  something like this could work:
http://www.amazon.com/HDE-Synthesizer-Microphone-Instrument-Converter/dp/B00D3QFHN8/ref=sr_1_6?ie=UTF8&qid=1447854681&sr=8-6&keywords=midi+usb+cable
 
beware, MIDI/USB cables which are cheap may not work well.  I paid $30 for my first one and it worked well.  others who paid less for cheaper models have not had as good luck.
 
so connect the ketron MIDI output to the cable and the other end of the cable to the computer via USB.
now set up an audio track in MC to record the input from the USB cable coming from the ketron.
set the OUTPUT of the MIDI track you just recorded to the INPUT of the ketron via the ketron USB connection
arm the audio track and hit record on the transport.
this will send your edited MIDI to the ketron and will send the audio from the ketron to MC and record it on the audio track without latency.  
 
this will work regardless of your latency buffer settings in your soundcard.

Thanks, Beagle. This sounds practical. I'd not gotten back because my attempt to setup the latest driver for Behringer x1204USB met with a dialog box saying This app can't run on your PC; contact the publisher, and I'm waiting to hear from them. But, as you say, if the mixer isn't working through USB, then it wouldn't matter. 
 
If this works, it will leave me wondering why the industry is all about USB umbilical cords feeding and pooping the baby devicers hooked to the mother, when you still have to plug and unplug and reconfigure for whichever step you're on in the recording process. I'll bet an Indian nickle some engineer is right now thinking up a more complicated way.