AlChuck, can you upload the file so some of us can look at what you are doing?

Cool.  I was just starting from the baseline.  It is probably something simple and silly - done that plenty of times.  My guess is probably something in the routing.  I can't imagine audio drivers interrupting one track.
 
The file might be handy, as well as your computer specs.  Again, I can't imagine a lack of cpu causing just one track not to play, but you never know.  Technology at work for us.
 
@

MarioD, I'm at work, away from my DAW, but I'll put something together tonight if I can squeeze out the time, assuming I don't figure out the routing issues when I take another look.
 
AT, I put my specs in one of the earlier posts. I don't think that is the issue at all, but I'll repeat them here:

 
SONAR X3C Producer (64 bit), Windows 7 Home Premium (64 bit), custom-built PC with Intel Core i5 CPU 3.10 Ghz, 16 GB RAM, Echo Layla 3G audio interface (PCI), Seagate ST1000DM003 hard drive (1 TB), Western Digital WD5000 hard drive (500 GB), Intel HD graphics

OK, so I created a new project. I created four MIDI tracks by recording one pass of some keyboard fiddling, and pasted the data into the additional tracks. I inserted four different synths -- Dimension Pro, Rapture, Session Drummer, and sfz+. I let each create a Simple Instrument track. I then assigned assigned each MIDI track to one of the synths. All voices play, no problem, just as I would reasonably hope and expect. I can solo each one and hear it in isolation, no problem. 
 
Then I go back to one of my existing projects with pre-existing MIDI data, with most parts assigned to the TTS-1. I insert Dimension Pro and assign one of the tracks to it. No sound from that track. I've uploaded that track at
 

 
if anyone wants to open it up and see. 
 
So I start to wonder if it's the presence of the TTS-1 that's the problem. So I take another pre-existing MIDI track and start inserting and assigning synths like in my first test project described above. Again, all voices play, together or when soloed. I insert a TTS-1 track. It, too, plays fine. Then I insert a sfz+ track. No sound.
 
I do seem to have gotten a lot further than before, and the results are encouraging, but I'm still puzzled why the Dimension Pro doesn't make any sounds in the one project and why the sfz+ doesn't in the other. I'm sure it's not just random happenstance, there must be something I'm doing wrong...

Don't know why there's blank space there where I put the link to the file - it showed up when I previewed and tested the link. Here it is again:

Oh, just noticed the "Some restrictions apply to prevent link (URL) Spam" message below the Submit Post button. I seem to be three posts shy of being allowed to post a URL.
 

Glad it is working better.  I just thought you might peek at the midi info page and see if anything strange crept into your problem song.  But keep at adding post.  Just don't try 3 quick posts - the forum software won't let you do that, either.  ;-)

Thanks, AT. I tried to PM you the link also but the same restrictions apply as to typing a URL in a post. (One down, two to go!) I'll open those files up again and look at the MIDI info as you suggest.

AlChuck you have a PM.

OK, I've passed the 25-post threshold so I can now publish the link to one of my troublesome project files:
 
http://alanoehler.com/seal-crazy.cwp