Here's my take (I have a 9900).
My problem was similar to that stated by so many... new cartridge inserted, followed by an "error" message. And I took the same steps suggested by so many: I burnished and cleaned the contact (using an eraser followed by alcohol & Q-tip): I tapped the cartridge on various density hard surfaces; and I made a mess by trying to release any air bubble(s) with the straightened end of a paper clip (some of the ink got released into the interior of the cartridge case - ugh). I alternated between these three strategies repeatedly over the course of hours. Nothing worked, no luck.
I did notice something that no one seems to have mentioned:
When inserting the new cartridge, the bar display in the window would indicate "100% full". That was encouraging (suggesting that the contacts were clean and being read by the printer). But my next step (printing out a nozzle check) inevitably resulted in an "error" message, immediately followed by the bar display in the window going down to zero with a mocking "X".
This suggested to me that the problem was not the contact, but air (or whatever) in the cartridge. After dinking around with this for hours last night, I settled on one last thing: setting the cartridge on end on my table, with the hole upward, thinking that any air bubbles might need time to work their way up through the somewhat viscous ink and rise to the hole. I intended to let it sit overnight, and then "burp" the damned thing in the morning before calling Epson.
This morning, I tried inserting the cartridge before burping (and then calling Epson in a panic) - and it works. My conclusions?
1.) Diagnosing whether a cartridge error is based on the contact, or on an air bubble, might be determined by whether or not the printer initially registers the cartridge as "full" (before trying to print anything). If it doesn't register, then it's probably the contact.
2.) Reasoning that the cartridge has been bounced around during shipping & subjected to all kinds of variations in temp, barometric pressure & humidity, I'm resolving to let it sit for a day to relax and to get used to its new surroundings. Treating it like a good red wine & exercising some patience might not be a bad strategy. Maybe it's significant that the cartridge shipped out of Dallas and was delivered to me three days later in Albuquerque (5000 foot elevation difference, low humidity, temps in the 95-100 degree range, and it probably spent the night in an air-conditioned UPS warehouse before spending hours in a hot UPS truck).
3.) Enormous stress might've been avoided. I've had a couple of jobs stalled since before the weekend pending getting this cartridge. My customers were already impatient, and I'd foolishly promised that I'd have their prints ready last night (knowing the new cartridge was scheduled for delivery yesterday, and figuring that I'd simply replace it & get straight to printing). From now on, I'm planning on ordering early enough that I'll have at least 24 hours lead time, after cartridge delivery, before planning on getting any promised prints out.