If you are using an HP LAserJet printer or similar it may be beacuse the printer in in a power-down or sllep type of mode, this can happen typically when no one has printed to the printer in awhile, and you can see on the display of the printer that is has entered this mode. The document will print eventually, after the printer "wakes up" and goes through a warmup routine. Another way to do this if you do have an HP, take the printer offline and reset it by clicking the shift and the reset keys on the fromt of the printer, this will cause the printer to undergo the warmup and print the pending documents. If I am thinking correctly then Canon printers have a similar "sleep" mode.