From The Jargon File (version 4.4.7, 29 Dec 2003) :
octal forty /ok'tl for?tee/, n. Hackish way of saying ?I'm drawing a blank.? Octal 40 is the ASCII space character, 0100000; by an odd coincidence, hex 40 (01000000) is the { EBCDIC space character. See wall.