Copy/Paste MIDI issues

[Mad Genius Audio]

Hey all, I've been working on this big project, playing an entire score into PT via MIDI to create a soundtrack for a high school to sing to. My issue is that throughout the course of this project, if I go to copy and paste MIDI data from one track to another, at times it works just fine, and at other times the Paste function simply isn't happening (or the Copy function, not sure). Nothing shows up in the intended Paste track, and it gets quite frustrating. I've had to trash the prefs many times over this project, I did just yesterday. Any thoughts?

[filosofem]

When performing the operation Copy & Paste is Keyboard Commands Focus enabled for the relative edit window or are you using a modifier? Posting OS X and Pro Tools version would help. Also can you reproduce this behaviour with a newly created session?