I just came across this note in my office!
Date of writing: Sept. 9th, 2015
In exactly one week from today, and then a week from that date and then another week afterwards, something will happen that causes certain badly designed computer programs to function improperly on those days.
It happens those three days and no other days in the year 2015. In any given year it will happen in exactly three days out of the year.
What might this finicky event be?