Continuity: In the beginning scenes, where Milo Thatch is practicing his proposal, he slides over (face forward, chest against the board) a chalk drawing of a map detailing the location of Atlantis.  When he realizes he wiped off the drawing, and sees it on his clothes, he stands in front of the blank part of the chalkboard, "filling in" the space with the map that rubbed off on his shirt -- the only problem is, that the image should have rubbed off BACKWARDS as he was FACING the board when it transferred to his clothes.   He could not simply stand in the place of the missing map face forward and have it read properly.

Continuity: In some scenes the adult Atlantean princess has some of her hair tied up at the back but the next minute it is all down.

Continuity: When Milo is speaking French to Kida, Milo is between Kida and the rest of the group, but in the next shot, when Mole talks to Kida, Mole and Kida are within feet of each other with Milo nowhere in sight.

Continuity: When Milo wipes the chalk off of the board onto his vest, he is shown with his vest completely closed. Just after that his vest is completely open and then closed again in the immediate next scene.

Continuity: When Milo is practicing the lines for his speech, a shield is leaning against a wooden pedestal. There are quite a few differences in the shield between when it is first seen and when Milo picks it up about a minute later. It's much smaller and flatter, the colors are darker, and the grey ring around it is wider.

Factual error: Languages are not directly translated to each other by letter to letter. There's no way that Ireland could be mistranslated as Iceland. In fact whatever language that fact was written in most likely had completely different words for Iceland and Ireland then we have today.

Other: When Milo is practising his speech, he jumps over the blackboard to answer the phone. The top of the blackboard rests on the desk, but when he slides back over, it swings all the way round . If it hit the desk one way, it would have hit the desk swinging the other way round.

Continuity: When Milo and Kida are trying to figure out how to power to the vehicle using Kida's crystal, the crystal is removed from around her neck to power the vehicle. However, in the next shot the crystal is back around her neck, still powering the vehicle. Then in the next shot the crystal is missing again, but replaced in the next shot, once again.

Continuity: When Milo is emoting to Sweet about how he is the reason that Rourke got the crystal, he goes to and sits on a red barrel shaped thing. When he first sits down, his bag is slung over his left shoulder (HIS left not OUR left), but in the next shot, it is slung over his right.

Plot hole: There is no way that 'COAST OF ICELAND' could ever have been mistranslated as 'COAST OF IRELAND'. For this to have happened, they would have had to have thought that the 'C' rune was an 'R' rune, but they had already deciphered the word 'COAST', so they knew what the 'C' rune was. Anyone would have worked this out in seconds, yet Milo says that people thought for a long time that the runes said 'COAST OF IRELAND'. While people might argue: "That's because the runic language isn't a direct letter-by-letter translation of the English language", read the runes above 'COAST OF IRELAND'. The 'O's are the same rune and the 'A's are the same rune, plus there is one rune for every letter, so it IS a direct letter-by-letter translation.

Factual error: Milo says Audrey is a "teenager". Which she is, but this is 1914! People didn't use that word back then. He probably should have said "adolescent" or something.