Sounds to be something wrong with the driver, maybe you don't have the correct one for that printer.
On my computer at university (Ubuntu 10.04) I have a HP laserjet with a huge variety of paper sizes which installed the HP driver automatically.
This may be because when I found the printer it went looking for the drivers and found them.
Your printer make might not be quite as popular as HP so it may not have found the drivers.
Where I would start, is by trying to find out what driver you currently have, then searching google for your printer make and linux driver. Or maybe just re-installing the printer (by removing and adding it again) and seeing if it finds the correct driver (make sure you're connected to the internet when you do.
Don't do anything that you're not sure what it does and/or how to undo it though based on my advice, I've never been that good at sorting out printers.