The Mariner 1 - 1962
A booster went off course because a programmer forgot a comma

Mariner 1 was the first spacecraft of the American Mariner program, designed for a planetary flyby of Venus. It cost $18.5 million in 1962. It was launched aboard an Atlas-Agena rocket on July 22, 1962. Shortly after takeoff the rocket responded improperly to commands from the guidance systems on the ground, setting the stage for an apparent software-related guidance system failure. With the craft effectively uncontrolled, a range safety officer ordered its destructive abort 294.5 seconds after launch.

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The booster had performed satisfactorily until an unscheduled yaw-lift (northeast) maneuver was detected by the range safety officer. Faulty application of the guidance commands made steering impossible and were directing the spacecraft towards a crash, possibly in the North Atlantic shipping lanes or in an inhabited area. The destruct command was sent 6 seconds before separation, after which the launch vehicle could not have been destroyed. The radio transponder continued to transmit signals for 64 seconds after the destruct command had been sent.

The Mariner 1 Post Flight Review Board determined that the omission of a coma in coded computer instructions in the data-editing program allowed transmission of incorrect guidance signals to the spacecraft. During the periods the airborne beacon was inoperative the omission of the hyphen in the data-editing program caused the computer to incorrectly accept the sweep frequency of the ground receiver as it sought the vehicle beacon signal and combined this data with the tracking data sent to the remaining guidance computation. This caused the computer to swing automatically into a series of unnecessary course corrections with erroneous steering commands which finally threw the spacecraft off course.

IF (TVAL .LT. 0.2E-2) GOTO 40
DO 40 M = 1, 3
W0 = (M-1)*0.5
X = H*1.74533E-2*W0
DO 20 N0 = 1, 8
EPS = 5.0*10.0**(N0-7)
IF (IER .EQ. 0) GOTO 10
DO 5 K = 1. 3
(When It had to write: DO 5 K = 1, 3; A comma for a point)