You'd often get the error when there was paper in the printer though. Turns out the cause is the slightly different size between US letter page size and A4 page size. Technically the printer's correct to complain (for the same reason it'd be correct to complain about an A4 sized print while full of A5), but virtually nobody gives a shit about that difference and so the "PC Load Letter" message just translated to "You have to push that stupid button before I'll do anything because pedantry."