[ALUG] Printer XXX may not be connected message, but it works

I have an HP Laserjet 1320 printer connected to my network via the USB port on my router. When I print to it I get a pop-up message saying:- Not connected? Printer 'LJ1320' may not be connected However the printer does work, if a little slowly. Does anyone have any idea what's causing the error message? -- Chris Green