My XP printer stopped working and the error on screen was the ink pad is at the end of service life contact Epson support. For £10 and about an hours work it's simple and very cost effective for any DIY enthusiast to do the same. See below and the end of the video to see where I ordered the new ink pads from and the access code needed to reset the printer.
Video covers XP-500, 520, 540, and XP-600 to XP-860 models (XP-510, 530 use same pads but different installation approach).