Thanks for posting your question. The problem you are facing is cause due to defective sensor switch, which detect the position of the tray. It is a micro switch, which send signal to the main board, when you put paper on the tray or the tray is inserted in the printer. If you have not tried to remove and reinsert the tray then, do it once and check the result. If you face the same problem then, unfortunately the sensor is defective and in that case the only solution is repairing the printer, as the sensor is a non user replacable part.
Please let me know, if you need any further information, otherwise please remember to give postive rating below, as that is the only way I am compensated for my time and effort.
See, honestly speaking this type of repair job is very easy for any trained tech, but I do not know how much time they will take to increase the repairing cost.