"Unable to Open Audio Playback Device" Error Message

I'm having trouble with an error message.  I'm using a church-owned laptop which I connect to MIDI instruments (an organ and digital piano) using two M-Audio USB 1X1 units.  I need to record MIDI only.  I do not have a MIDI implementation guide for the organ and have to record MIDI messages to determine how the pistons and crescendo pedals work.  Unfortunately, I cannot even get to the point where Sonar will record MIDI data.  The "Unable to Open Audio Playback Device" error message appears after I arm a MIDI track in a project that has NO AUDIO TRACKS and set it to record.  I do not know how to get around this.  The laptop has a sound card (Realtek High Definition Audio) but some audio setting must be incorrect.  Sonar will not let me disable audio so I'm dead in the water.  Can someone explain the problem and help me get past the error message?

Also, I'm not sure how Sonar would deal with 2 USB MIDI inputs from 2 interfaces. Used to be you had to use a MIDI merge box if recording from more than one source at a time. Or are you only recording one instrument at a time?
As Beagle says, use MME mode and in MIDI options  set your output to the MS wavetable or to the M-audio if your planning on feeding the MIDI back  to the original intruments. Later you can playback using the soft synths (TTS-1)  but that usually means having better drivers than the Realtech.

Beagle & johnnyV,
 
Selecting the MME option worked.  Thank you for the suggestion.  MIDIOX is on the laptop, too, but I really needed to capture the information in SONAR.  I'm not familiar enough with MIDOX for this type of problem, anyway.  In the past I created a large number of sequences that drive Roland synths, which I have been able to adapt to the organ and digital piano at church.  Since the sequences were almost all for accompanying the choir (I don't have the luxury of a live accompanist), I had to figure out an efficient way to run rehearsals without dragging a bunch of equipment to the facility.  We only recently started renting the building and it has a very nice Allen organ and decent digital piano.  Using these instruments is much more convenient than hauling my gear!
 
At any rate, I can drive the organ and piano with existing sequences but without a MIDI implementation guide, I have no idea what banks, patches, RPNs and NRPRs to send.  Consequently, when a sequence starts it sets up the organ with a very loud set of stops and usually puts the crescendo pedal on full blast as well.  I have to run the organ and change to a more appropriate piston or it makes people jump about two feet in the air!  Thus, it is critical for me to record what happens when a piston is selected, when stops are added or subtracted, when tutti buttons are pushed, when couplers are used, when the crescendo pedal is pushed, etc.  There is vitrually no information available on these things so trial and error are necessary.
 
To answer your questions about the MIDI setup, I am using two M-Audio USB 1X1 adaptors, each in its own USB port, and SONAR has no problem distinguishing between the two instruments.  They are simply identified as something like "USB Out 1" and "USB Out 2" and it works.  Once I can record MIDI I will be able to effectively control each instrument with correct voices.  Also, please note that I'm not recording from two instruments at the same time so there's no problem there.
 
Once again, thanks for the recommendations.  I will finally make some headway this weekend!
 
UCG Musician

johnnyV,
 
Yes, that was me!  And I re-read the suggestions I had gotten back then before posting again.  Some parameter must have changed in the Audio set-up and the error message reappeared.  Also, please note that I only get access to the instrument once per week and most times I'm there I don't get an opportunity to experiment with the equipment because I have to run choir and orchestra rehearsals.  I did not have a key to the building, either, so it forced other people to wait for me while I did this sort of stuff and that was not a good situation.  I have since been given my own set of keys and now no one has to wait for me to lock up the hall.  I am optimistic that after all these months of making little progress it should finally be possible to get my arms around the problem!
 
UCG Musician