Factual error: At the beginning, the MacManus brothers are attending a Catholic mass. The priest is saying the Our Father, and concludes it with "For thine is the kingdom, the power, and the glory for ever and ever." However, Catholics do not include this line when they say this prayer - only Protestants say this. Also, the prayer is never said before the priest gives his homily as it is in the movie.
Factual error: In the scene, where Paul Smecker is checking the green trash-bin, he finds a bullet from Ivan Checkov's gun. Nevertheless, earlier (in the plot), or later (in subsequence of the scenes), in the scene, where Connor MacManus is falling down with toilet on Russians' backs, Ivan Checkov, while the toilet hits his bald head, is shooting with his gun, but he misses the trash-bin - the angle of shooting is obviously too extreme to hit the bin.