Q: Lexmark Pro 915 Airprint Support?

Good question - The Apple Store indicates AirPrint compatibility as well as AirPrint Basics which leads me to believe it should work without any trouble at all.

However, Lexmark's manual does not mention AirPrint except to indicate Apple's trademark. This seems like an odd omission to make.

Your wireless router is an integral part of AirPrint communication. All Apple AirPort Base Stations support AirPrint (obviously) but some others may require a firmware upgrade, as long as they are not too ancient. A couple are known to be incompatible with AirPrint.

Try resetting (power down) your iOS device, your router, and the printer.

What make you say that it isn't supported?

I also note you state you have "915A". "915" is what is listed on here: http://support.apple.com/kb/HT4356. May not be the same printer.

This might be the problem:

Firmware for the Pro 910 Series. Provides Apple Airprint Capability.

Update your Lexmark's firmware:

http://support.lexmark.com/index?page=content&id=DR21242&locale=EN&userlocale=EN _US