I don't know what the source of your problem is. Dana or Kelly may. In the meantime, based on my reading and my own printer here are some things to try. Google may suggest others, although your precise message didn't show up for me:
. A worst case possibility is that you've installed Epson software and allowed it to update the driver and/or firmware, and now it won't recognise 3rd party carts. This is especially an issue on Macs I believe (I'm on Windows). Is there any chance that you might have done this? If you have, Jon claims that it can't be undone, although you'd think that a driver could be downgraded, but probably not the firmware. See this thread for a recent discussion, especially towards the end. I don't know whether the issue applies to an R2880 as well.
. Cart not inserted correctly. Sometimes removing and carefully reinserting helps.
. Dirty contacts. Try gently cleaning with some pure alcohol like ispropyl.
. Has the printer recognised the cart switch? I did this switch in the last few days and had to go into printer preferences and tell it that the PK was now installed rather than MK.
. A faulty chip. Do you have another cart that you can test with? A resetter may or may not help.
Can you post a screen grab of what the Epson status monitor looks like? (See http://www.inkjetmall.com/tech/content.php?152-How-to-attach-images-to-this-forum )