I've had the same problem and have pretty much almost given up on EI's. It's great for those who will use it frequently but i don't and the ink keeps clogging.
There were some pretty good tips about storing the carts in ziplocs and rinsing the printhead after each use, but i need to get it to work again before i can get to the maintenance phase. I have rinsed the printhead, soaked it, had to refill carts consistently, etc etc. but i could not get the magenta to work. I've put it on hold for a while because the whole deal was way too frustrating.