It will probably have something to do with the fact that the LaserJet 1020 is a 'host-based' printer.
Many models of this type of printer (also sometimes known as a 'GDI', or 'Windows' printer) are NOT supported via print servers; I've no idea if this is the case with this particular model, although the HP document
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&docname=c00381599&dlc=en&lc=en&jumpid=reg_R1002_USEN seems to imply (perhaps somewhat ambiguously) that it is not.
I have seen reference to some sites having success printing with such printers via print servers, if 'bi-directional' support is disabled.