AirPrint says printer is offline, but it isn't.

I have selected my HP Photosmart Plus B210 for AirPrint, and the iPad says that it is contacting the printer, and then even preparing the pages and sending to the printer, but it doesn't print. It says the printer is offline, but it isn't! I can print wirelessly to it from my desktop. I have rebooted the iPad and the printer. Any suggestions?