This has happened from time to time for me, so now I want to know what the deal might be. All of a sudden a midi track becomes grey instead of it's usual color and I'm not able to cut/paste in it. I've search for "lock track", but it does not have the "lock" symbol on it. I've tried tp clone in different ways, but the new track is also uneditable. Any idea what might have happened ?

Wish I could help but I have this problem, too, where cut/copy/paste stopworking.  Also sometimes can't split clips.

have you done any region FX editing to these tracks ?
you need to bounce the track "Bounce to clips" before you can edit it.
 
 
Never mind its a midi track. Have you made multiple takes on these midi tracks ?

I have the same problem! I try to move some midi data from one midi track to another using cut and paste but nothing happens..  I tried in staff view, in the track view using clips and using paste special, but it won't paste anything...

SoundRegion
All of a sudden a midi track becomes grey instead of it's usual color and I'm not able to cut/paste in it.

Looks like you accidentally hit "K" with the track selected, this triggers "clip mute" and turns it grey. Not sure if this is related to the paste problem...