I keep running into this problem.

1. Have a song composed.
2. Have a track available, (strings, "white color")
3. Right click/assign real track player, (i.e. Guitar, country cowboy 165)
4. Generate track now
5. Nothing. . .
Track stays unassigned, no RT player??

6. Tried erasing track, thought there was some latent data on there, or something. . .