Factual error: When the Americans are driving Lars to the contest, after spinning out, the driver puts the car in second gear (pulls the shifter back) instead of first and then speeds away from a standstill. Second gear would not sound like it did in the movie plus the acceleration would have been very weak, possibly stalling.
Continuity mistake: Lars jumps into the summer water while wearing yellow pants, comes out wearing red, and is back in yellow pants on the flight back to Scotland.
Factual error: Considering Sigrit and Lars are similar ages in the opening flashback to 1974, 41 year old Rachel McAdams should be a similar age to the 52 year old Will Ferrell, which she clearly isn't. Alternatively, if she's meant to be in her 50s, there's no way they'd have been able to have a baby together.
Factual error: During the voting in the first semi final Spain, Germany and Spain are listed on the scoreboard. These three countries are, as members of Eurovision's "Big Five", automatically qualified for the finale.
Factual error: During the semi finals of Eurovision there is no voting procedure like in the final with every single country presenting its jury vote. Instead, only the ten qualifiers for the final are named in a random order.
Factual error: A central point of the plot is Iceland not being able to host due to financial constraints. But the winning country is allowed to nominate another country to take on the hosting role if wanted.