Well, you can drag that midi track to your desktop and it will create a midi file. You can then close the project in Sonar, then go to File>Open a Project and literally open the midi file. Sonar will automatically insert TTS-1 and you should be able to just hit play and have it work.
Alternatively, you could drag the midi track off to your desktop, again this will create a midi file. Then, close the Sonar project. Start up a brand new Normal project, insert a midi track, import your saved midi file to that midi track, then insert the soft synth of your choice, load up a patch, insert a couple of mono audio tracks or a single stereo audio track, make your input/output assignments for the soft synth and the audio tracks, and it should play fine.
I would think either of the 2 methods would circumvent whatever you might have done to the original project where it doesn't want to play. (either of the 2 methods puts you into a new project - just 2 different approaches to it).
Perhaps there is a midi channel issue with the original midi track, where you would need to look at the events and match the midi channel of the soft synth to react to the midi channel(s) in the midi track). Just a thought there.
I hope that helps,
Bob Bone