Ug - I'm now having this problem.
Canon Selphy CP510 was working fine on my MBP & I decided to move it to the Mac Mini - both have latest OS X Lion installed, with all updates etc.
On the mini I can see the printer when I click the '+' to add a printer, but no driver is listed or available.
I've downloaded & installed the Canon driver, but still no joy
I've also unplugged & re-plugged in the printer to see if the Mac will pick it up.
Any ideas ?