I was around for the gold master of AOL 5.0 (Kilimanjaro). After the release we were pulled into a conference room to get on a call with Steve Case. You don't want to get on a call with the CEO immediately after a launch. It turns out our execs were installing 5.0 and then... couldn't get online. It hung with the modem init. As the person in charge of the QA lab I pulled all of our test run data. Couldn't duplicate on any of the dozens of machines. Sr. devs were running debuggers. Didn't see anything on their machines. We went into the office of our highest-level exec and borrowed his laptop.

Winmodem. Dev hooked up a debugger and found the issue. There was a bug in the soft modem driver. Hot fix was released, but it was too late for the pressed CDs. Luckily it was an edge case on high-end laptops. That were issued to all of our execs with the buggy driver.

Good times.