AirPrint works with iPhone but not iPad?

I bought an HP Photosmart 5515 printer for the sole purpose of being able to print via AirPrint from my iPad 2. It does not work and follows an outline of the problem.

Printer appears in choose printer on iPhone.

Sending an item to print opens a dialogue "connecting to printer". Followed by "preparing to print" and a page count if more than one page.

Dialogue closes but nothing is printed and there is no visible response from the printer.

I am able to print from the iPad using HP's "eprint" service, documents, web pages and photos.

I am able to print via AirPrint from my iPhone 3Gs.

This seems to rule out a problem with the printer and the wireless network. The iPad can see the printer but fails to send the job. As the iPhone works perfectly it appears the problem must be with the iPad.

Any ideas on what may be blocking this or is there something really simple I have missed?

Alan