Character mistake: In the scene when Dave is checking out the failed transmitter at the radio station, Dave says "the bad news is your return loss - way too high". This is a mistake, as the movie makers got confused between the terms "return loss" and "insertion loss". Dave should have correctly said either "your return loss - way too low" or "your insertion loss - way too high".
Character mistake: After Gru tucks the girls in for the night, Dr. Nefario tells him that there are 48 hours until the rocket's scheduled launch. The rocket launch, then, should have taken place at night, around the time the girls go to bed, two days later. The rocket, however, launches during daylight hours.
Character mistake: Throughout the film, the characters refers to the seigneurie as Beaufort or Beaupré, which are actually two different places.
Character mistake: Tool neglects to dress Barney's tattoo after he completes it. Not something a professional tattoo artist would neglect to do, especially when he is tattooing a friend.
Suggested correction: Tool states that it's taken him several months to do the logo tattoo. It's also implied that he has done the rest of Barney's tattoo's. Barney, being the tough man he is, could have simply said in the past not to bother with dressing it and Tool has done as told against his better judgement.