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Either a switch (sensor switch, that is, one that senses the presence of paper) is jammed in the ADF feeder on top of the printer - or else, there is a problem with the circuitry of the printer, that causes a completely fake error.
Open the ADF feeder. See if you can spot a small paper sensor switch that is fouled, broken, jammed in the 'on' or depressed position, etc., anywhere in the ADF feeder's paper path.
If nothing can be seen, then I regret to say, it's a choice between repair-servicing the printer, or replacing it, most likely.
If you can think of anything else distinctive that the printer has been doing, let me know, please, and I will advise you further.