Most coding horror stories pertain with unmaintainable code. (Or with unmaintainable and horrific piles of garbage.)
(Then again, the story here sounds incredibly familiar. One guy builds version 1 in a few months and then a team of 15 can't build version 2 for years and years. Tell me you haven't seen that movie before.) -- Joel SpolskyOne of my personnal horror stories is about a web forum software bought from a small french company -- one big Perl/CGI script, without docs. I had to maintain it, at a time the company had disappeared -- not suprising, considering the very poor performance of their software. At this time I wrote from scratch a free clone of it. Sometimes that's the better way to maintain. (Don't look too closely at it, I'm not particulary proud of this software -- but it's way better than the original crap.)