Source : Free On-Line Dictionary of Computing

line 666
     
         (Christian eschatological myth) The notional line of
        source at which a program fails for obscure reasons, implying
        either that *somebody* is out to get it (when you are the
        programmer), or that it richly deserves to be got (when you
        are not).
     
        E.g. "It works when I trace through it, but seems to crash on
        line 666 when I run it."  "What happens is that whenever a
        large batch comes through, mmdf dies on the Line of the Beast.
        Probably some twit {hard-coded} a buffer size."
     
        [{Jargon File}]
     
        (1999-03-01)