This is a firmware error.
Usually, the culprit is a print job that is “confusing” your printer.
First, try disconnecting the printer from the computer (or from the network.) Then, turn the printer on and see if it comes to ready. If it does, remove every job in the print queue–on your computer or the server–so that nothing is waiting in the queue to be sent to the printer. Finally, turn the printer back on and see if the error message is gone.
If you still get the same error message, check the driver you are using and switch to another. You may need to update your driver.
The last thing to try is a firmware upgrade. This can be done by visiting hp.com and downloading the proper firmware version for your specific model of printer.