Hi, I think I am missing something basic here - one track is not playing properly and the notes in the event list are shown in gray text. The piano roll shows the same notes without any internal color, just the outline.
 
What does this mean?

This sounds like the midi clip is muted.  Highlight that clip and press K this will un-mute the clip.

Check the clip or notes aren't muted. A muted clip will produce those results.
 
HTH

Beaten to it by a fast typing Wookie. 
 

FastBikerBoy
Beaten to it by a fast typing Wookie. 
 

Sorry FBB I was just swooping past and for once the furry paws did not get caught up in the keyboard

Nope, nothing Muted, I had thought of that. True, the notes don't make a sound, but if you click on them in PRV, they do sound. Also the Kontakt on screen keyboard sounds for the player, so not muted per se.
 
Also, new notes added are not grayed out. Copying and pasting one of the grayed out notes results in an additional grayed out note. There is some property on the individual notes causing this.
 
I just tried using the mute tool to mute and unmute notes that I added afterwards as a test, and they change to the same outline-only view in the PRV, but they do not change to gray in the event list. Re-clicking on those added notes unmutes them, but the pre-existing notes remain "unimpressed" by the unmute button and don't change. This is something different.
 
Any other ideas?

I had a similar thing and it was a midi track with take lanes, the unsed takes show up as gray the best I remember. If it is a track with take lanes then collapse it down to single track by closing take lanes and look again it should only show the notes being used , if that is indeed what is happening.
 
I should clarify this is how it behaved for me in the piano roll view, I assume that the event list would behave similarly.
 

AH! Take Lanes! Thanks Teego - this looks the likely culprit.
 
 

Did you solve this in the end? Was it due to Take Lanes?
 
I experienced something similar yesterday. Notes were greyed out in PRV, although the corresponding midi clip was displayed normally in Track View. I eventually got rid of the problem by deleting that instance of PRV (which was one of several, docked in the floating Multidock) and opening a new one. The new one was fine.  Take Lanes were not present at all in this project.

Hi Kev999 
 
Yes TakeLanes was the key, but I ended up having to delete some of the lanes because I could not for the life of me get them to be accepted as part of the overall track. When I re-recorded the stuff in the take (in this case just CC events) it worked fine. 
 
There are definitely some screwy things going on - some midi notes won't play but if you move the start point a fraction they will play. Everything seems a little fragile.
 
But yes the immediate problem I had has gone.