I had a most unusual experience last night while working on a piece.  The MIDI sequence has about 32 instruments, there’s no audio yet in this file, and no software synths or plug-ins, just MIDI data.   Suddenly, the harp won’t play back.  I can play the instrument on my MIDI keyboard, so I know the instrument is being triggered. The notes are in the staff view, I can click on a note in the staff view and hear it, but no notes in the track will play.  The track is NOT muted or archived, all velocities are within normal range, and both controllers 7 and 11 are at 127.  There are not hidden events as I applied “trimming” and “bounce to clip”. 
 
But the really strange thing-- I’ve never seen this before—is that in the event list all notes, patch changes and controller data are “greyed out”.  I can see the data but it’s like the data isn’t there.  I also saw something I’ve never seen before, in the track view, when examining the MIDI data display, there appeared a little red circle with a diagonal line running through it, which I took to mean a corrupted track, but not really certain.   I tried cloning the track, but the cloned track had the same issue.  I created a new track and tried copying and pasting music to it from the corrupted track, but this too wouldn’t play.  So, I went ahead and re-entered all the data by hand, luckily having the staff view notes to copy from manually.
 
Has anyone seen this before?  In the 27 years I’ve been sequencing music, I’ve never seen this.  
 
Thanks,
Jerry Gerber
www.jerrygerber.com
 

The little red circle with diagonal line means the clip is muted.

there appeared a little red circle with a diagonal line running through it,

 
This indicates the clip is muted not the track, highlight the track and press K the circle will go away and the data will now sound.