Hi Greg~
Thanks for the feedback, I'm sorry to hear the new carts didn't solve your problem. It's curious that you're having trouble with these two positions, after trying two different refill carts and chips, because all the carts are made from the same mold (so are the same shape/size), but have different chips specific to the color position. If it's a physical fit issue causing your trouble with these two positions, then I would think you would have issues with other position carts, or would have different results with the two new carts. The fact that you're consistently having errors with these two color positions after trying other refill carts and chips, but the error goes away when you install Epson carts- tells me the chip sensors are working, but makes me think something is preventing a good connection with the cartridge chips and chip sensors...
We don't have any Epson carts here for you to try, but I did find a few older model refill carts for the 4800. After examining/comparing the two cartridge designs, I see the plastic exit valve cover of the current cartridge sticks out and the previous model exit valve cover is flat/flush with the cartridge face. Although we've had good results with these carts (we're using these carts in our 7600 here, with the chip sensors disabled- since the 7600 uses the same style/shape/size carts as the 4800/4880, but with different chips), and have been selling this model cartridge for nearly two years with good feedback/results, we've never been concerned about the exit valve cover, but now have two reports of what seems to be the carts not going into the printer all the way, which I wonder may be due to the exit valve cover... Have you tried pushing all the refill carts into the printer with more pressure, evenly pushing on all four carts on one side, while lowering the locking lever?
I have two ideas to determine what's causing your issues:
1. Transfer the chip from the Epson cart to the refill cart (instructions below) and insert the cart to see if your printer displays the error or not (this is the quickest/easiest thing to try), and if you do get the error with the Epson chip,
2. I can ship you a prior model cart (with flat exit valve cover) to try.
Please let me know so I can help get to the bottom of this, and you back to happily printing.
Best regards~ Dana 
Attach Epson chip to refill cart
Before handling any chips (or really any electrical device for that matter), you should ground yourself and mindful of the clothing you wear, and if you're working on carpet, etc... as static shock can destroy a chip.
Looking at the chip on the Epson cartridge, you will notice there are two small plastic points that hold the chip in place. Make a note as to which way the chip fits onto the cartridge so you can attach it to the refill cartridge in the same direction. Using a straight razor blade at an angle carefully cut the top of these two points off (be careful not to scratch the gold contacts), which will release the chip so you can carefully pry it off the cartridge using the edge of the blade. You can also use a sharp knife or something similar to pry the chip off the refill cartridge. You will notice the same two points on the refill cartridge where the chip goes (pry the chip off the refill cartridge before attaching the Epson chip in it’s place)- gently line up the Epson chip with these points and attach it to the refill cartridge by using single thickness (not foam or thick) double sided tape. Making sure your hands are clean and dry, press the chip to make sure it is tightly seated and flat/flush on the cartridge. Now, using the chip resetter- reset the chip and insert the cartridge into your printer. NOTE: Installing a cartridge without a chip, or with a crooked chip attached can damage the printer's chip sensor- so always make sure cartridges have chips secured flat before installing cartridges
