Was this a case of bad
testing, or bad time management?
That said, a project group I worked with in university had created a networked game for a class. We had had a small communication problem before where the last-joined client wasn't in sync with the rest. We thought we'd solved that, until we had the demo. And guess which of the clients was the last to join? Of course, the one connected to the beamer...
An ex-colleague of mine at least had the brilliance (the only brilliance he's ever shown) to show all errors (and there were quite a lot of them) on the secondary screen instead of the displayed screen during his demo.