Xp Workstation randomly loses default printer

I have an office of 7 workstations setup the same way sharing 2 network printers One of those workstaations randomly loses the default printer. displayes message no default printer please select printer. it allowes you to select the printer and set it as default for a while then randomly does the same thing. The other 6 workstations are fine. So I believe it is workstation specific. Any ideas?