I have a project that I have been working on for some time, a mix of MIDI and audio tracks.  I opened it today and it loads fine, but when I hit play - it's stuck on 1:01 - it seems to be looping on the first second.  I'm not even sure how to go about troubleshooting this - my other projects play just fine.

That happened to me once, 
 
Turn if the looping option, Since it is stuck at the beginning, you can't see the yellow loop lines at the top.
 
Read this if you don't know to turn it off.
https://www.cakewalk.com/Documentation?product=SONAR%20X3&language=3&help=Tutorial1.8.html
 

I feel foolish now - I was looking for the loop section, but couldn't find it.  Your suggestion did the trick, thanks!

Glad I was able to assist.