Have you tried to restart the iPad and the printer?
This may help too -> iOS: AirPrint 101
Verify that the printer:
- Has power and is turned on. If it has power, turn the printer off and then on again to see if that resolves the issue.
- Is connected to the same Wi-Fi network as the iOS device.
- Has the latest firmware version installed.
- Has paper with enough ink or toner installed.
- Is free of any errors displayed on the printer's control panel.
- Avoid connecting AirPrint-capable printers to the USB port of Apple AirPort Base Stations or Time Capsules. Doing so can enable traditional AirPort printing from a Mac, but it will not enable AirPrint functions for iOS devices. If you cannot use Wi-Fi networking to connect the AirPrint-capable printer, use an Ethernet connection from the AirPrint-capable printer to the Apple AirPort Base Station or Time Capsule.
- Wi-Fi printers can take several minutes to join a Wi-Fi network after being turned on. Ensure that the printer is connected to the Wi-Fi network before attempting to print.
If it is telling you the printer is off line, there may be something stuck in the print queue, or the printer thinks its paper is empty. Or out of ink. Double tap the home button, and see if the print center shows up in the task bar. If so, clear any pending jobs, or see if it is giving you any other message.
Go take a hard look at the printer. It may be as simple as turning it off and on again. But see if it wants ink or paper. When in doubt, reboot the printer, the router and the pad.
Has it worked before? If this is a new set up, make sure you download and install the firware update that they all seem to need. Do it from the printer console if you can, avoiding the desktop software.