Continuity mistake: When Luther arrives at the monastery for his questioning, he arrives at night, and it is raining very hard. When he is ushered into the room with his mentor, Luther is still wet from the rain, but it is sunny outside the window.
Continuity mistake: After Luther doesn't recant his books at the trial, the Emperor's hand is up near his mouth in a close up shot, and in the next shot we see him in the background with his hand resting on his chair.