Thank you for using the Support Forum. please take a look at the solutions for not printing. I know you stated that the machine prints but these are some things to check for this intermittent error you are seeing. Pay particular attentions to solutions 4 and 7. If this does not help please consider contacting your support centre for further assistance.
We have a new(ish) Phaser 7800 that we've had the techs out to look at a couple of times. The printer is working but the indicator light on the front panel is red and we're getting an error message pop-up.