The encoder strip may have gone out of range of the sensor. Switch off the printer. Slide the cartridge carrier to the middle of the printer by taking the top part of the belt and moving it gently to the right. Place an index finger on the encoder strip on either side of the cartridge carrier. The encoder strip is a clear strip running the length of the printer, above or behind the cartridge carrier. On the back of the cartridge carrier, there is a small slot that the encoder strip fits into. Slightly push the encoder strip down and then back up to get it into the slot. Then lightly press the strip first to the rear and then forward, if necessary. Once you have placed the encoder strip back to its position, close the cover. Plug the printer or turn the printer on. Load your cartridge and try to print again.