I had a very frustrating problem with my printer - I think actually a firmware bug from Epson. It would go back and forth...

And here is the answer that even Epson support didn't know (they claimed it was a HW issue which it was not). There is a small rectangular slot on the front right of the cover. Gently push a screwdriver or the point of a scissor down into that and it releases the top! I was then able to replace the ink cartridges and all was well again.