Pet Bugs II - Debugger War Stories

AlphaHelix queries: "A few weeks back there was an article on Pet Bugs, where people were asked about their favorite bugs. I have a different sort of question: what was your greatest debugging challenge? I've been debugging for a long time, from analog circuits all the way up to multi-kLOC multithreaded servers, and I have some pretty grisly war stories, like the time I debugged a problem in a third-party DLL in machine code because the client didn't have the source for it (yay open source.) What was your greatest debugging triumph?" The first time Slashdot did this it was more about bugs that you had encountered (and may not have solved), this one is about bugs in your own projects code and the trials and tribulations you had to go thru to get them fixed.