"Remember that one bug that had you tearing your hair out and banging your head against the wall for the longest time? And how it felt when you finally solved it? Here's a chance to share your greatest frustration and triumph with the community.
One that I vividly recall occurred back in the early 90's at a startup that was developing custom PBX hardware and software. There was the current development prototype rack and another rack for us in Quality Assurance (QA). Our shipping deadline for a major client was fast approaching, and the pressure level was high as development released the latest hardware and software for us to test. We soon discovered that our system would not boot up successfully. We were getting all kinds of errors; different errors each time. Development's machine booted just fine, *every* time. We swapped out our hard disks, the power supply, the main processing board, the communications boards, and finally the entire backplane in which all of these were housed. The days passed and the system still failed to boot up successfully and gave us different errors on each reboot.
What could it be? We were all stymied and frustrated as the deadline loomed before us. It was then that I noticed the power strips on each rack into which all the frames and power supplies were plugged. The power strip on the dev server was 12-gauge (i.e. could handle 20 amps) but the one on the QA rack was only 14-gauge (15 amps). The power draw caused by spinning up the drives was just enough to leave the system board under-powered for bootup.
We swapped in a new $10 power strip and it worked perfectly. And we made the deadline, too! So, fellow Soylents, what have you got? Share your favorite tale of woe and success and finally bask in the glory you deserve."
I found a GPL violation in some code. The "developer" who violated it had changed *almost* all of the variable names. The few that he hadn't changed were odd, and rolled around in my head. This doesn't happen very often; but I actually had a dream that first led me to read a book with a similar title. Half way through the book I googled the exact text and found the offending code in an academic work that had just recently been crawled by Google.
I'm not sure if I should be proud or not of the way I handled it socially and administratively; but it was routed out. In fact, we ended up auditing everything which was a dull chore. No other problems found.
As far as real bugs go, the ones that are most challenging and always a relief to solve are the ones where one part of a C program steps on another. The actual point of failure is never where the bad code is, so you have to get real creative to find where somebody wrote into a structure "way over there" in another part of the code. I can't point to any one of those in particular though; just that general class of bugs always gives you a sense of relief and accomplishment.
AC to avoid dredging up hard feelings...