WNDR3700, with Backfire10.03
cups is installed in extended usb stick, and works fine -- other computers can use the printer.
Printing information is shown well at 192.168.1.1:631, the website is helpful http://www.delta-phi.net/?p=127&lang=en

However, there is a strange problem:

all cups instructions, like lpinfo, lp, lpadmin, lpstat and so on, do not have return values. It seems they do not work.

Anyone knows what is happening? Thanks~