Mike ~ Did you resolve the issue?
I'm using MagicMix ink and a CIS on a 1280 and I have the same problem from time to time.
You don't want to do continuous head cleanings or you'll destroy the print heads. Instead, do one head cleaning and print a page of black bars. Wait 30 minutes and repeat process. This will help move out any air bubbles – if that's the issue.
That normally works for me, but one time it didn't. I took the ink cartridges out and flipped them over for a few minutes and when I put it back in place it started working fine!

I think there was a tiny piece of plastic covering the nozzle or something.