9-9-99 was a date to which belonged a bug similar to the famous Y2K bug. 9-9-99 was used by many programmers in the past to indicate an error or invalid date field. The problem is that 9-9-99 was in fact a real date and when that date came some software would recognize it as an invalid field and would generate errors. It seems that when the time came people were prepared and little trouble was actually caused by this bug.