When I select the solo button on the midi icon for Superior Drummer 3 and then hit play...one of my other soft synths plays instead of Superior Drummer.  Also, if I unfreeze Superior Drummer I get no sound from them during playback.  If I undo the unfreeze the drums will play again.  Any clues?

Is SD set to output MIDI?

How do you have MIDI Echo configured?

Make sure the MIDI track hasn't been inadvertently re-routed to a different instrument.

bitflipper
Make sure the MIDI track hasn't been inadvertently re-routed to a different instrument.

Bingo...fixed...thank you!
 
I never go into those settings so it's a mystery to me how it got change.  I'm sure it didn't get changed on it's own...ghost in the box.

The easiest way to have that happen is to delete a synth without deleting its associated tracks.