May 13 was one of Uber’s darkest days.

The computer system used by its business-operations employees ground to a halt, for the whole day. The cause: a bug in one of Uber’s databases, which set off a chain reaction that took down other systems and was made worse by human errors in response to the cascading problems, according to internal emails reviewed by The Information.

Uber’s chief technology officer, Thuan Pham, later wrote to his staff that the mistake “reflects an amateurism with our overall engineering organization, its culture, its processes, and its operation.”