Satellite control software: you enter tiny time intervals using scientific notation to command very short thruster bursts for realignment. User A, the usual guy, always uses lowercase 'e', no problem. One day he goes on holiday, user B takes over, and on his first day enters a value using uppercase 'E'. The s/w is not expecting this, and so interprets 7.6E-3 seconds as 7.6 seconds (e.g., exact numbers unknown).

Fortunately, after the predicable mass panic, they were eventually able to relocate the satellite.