Midi file corrupted - crackling?

[micart671]

I have a recording session that seems corrupted. When i open the session i get a loud crackling in my monitors. It seems to be linked to a midi track as the track is not it's usual blue colour but grey (and un-editable).

I have tried copying and pasting the midi file to a new instrument track which works until i save, close and re-open again.

Any help will be greatly appreciated, ta