I cannot remember correctly the problem that led to some spacecraft missing the target some years ago.
(I can't even find it on Google® 'cause I really don't know what to search for!)
Anyway, there was a comma instead of a decimal point, or metric measurment where an English system was expected. Some thing that our eyes, when doing multiple error checkings, never notice, for it is right in front of us.
Do you remember the incident?
Mars??
http://www.freerepublic.com/focus/f-news/1801589/posts
Around #75
Mars Climate Orbiter:
http://mars.jpl.nasa.gov/msp98/news/mco990930.html
(I had friends flying that mission - sad time)