Thanks to Geoff Quickfall who originally posted it in this thread...
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cgi?read=197269#197269
You have to be quick and press all the keys in the sequence order fairly rapidly or you will get [ERROR 9].
Edited: 26 Sept 2011, 4:24 p.m.