There is a counter inside the printer, which counts the amount of use the printer has done. When this counter reaches a preset limit, it shuts the printer down and displays the message you have mentioned. There is a reset program on the net to reset this counter and enable the printer to work again. I cant remember the name of the program, but I'm sure you will find it, if you google r300 reset.
Turn off printer. Press stop, maintenance and power bottons at the same time.