This isn't really an engineering or a competition mistake, but last year for worlds, "someone" sent the robot to the headquarters of the shipping company (which is in Texas) instead of to the competition (which is in St. Louis, MO).
Spent about a month working on getting it to St. Louis in time, and even then we drove 13 hours not even sure if the robot would be there when we arrived.
Lesson learned, read the full packet on how to ship the robot instead of skimming through and using the first address you find.