Can browse to printer but not print!

I have a Lexmark networked printer, connected via Ethernet cable to a Netgear wifi extender. It has a reserved IP, and I can both ping the printer and access its built-in administration page via a web browser. So it's clearly connected, on-line, and accessible. But, none of my computers (Mac Pro 10.6, MacBook Air 10.8) can actually print. The errors are like "Unable to connect to printer..." or stuck on "Connected to printer..." - how do I debug this, given that the machine is up and accessible but won't print?