I used to work for a huge technology and engineering firm that was installing security systems for a new stadium. The deadlines for everything were written into the contract such that there were considerable penalties for not delivering portions of the scope on time. We were notified that we were in default of the contract for not installing the parapet cameras on the high perimeter of the stadium.

Our excuse was pretty solid: They had not finished building the stadium. There was no "top" of the stadium yet to mount anything on. It was fucking air.

We had to defend that for a few weeks before they backed off.