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How old is the printer?
Have you been using Epson OEM-original ink cartridges in it?
Has the printer had a period of disuse lately?
One thing to try: turn it Off, unplug it from the power. Leave that way for at least 1 hour (60 minutes), and see if that rest and reset helps it recognize the cartridge. This is not guaranteed to work, and need only be tried once.