Factual error: At the end of the movie the cast is counting down to the explosion of the Krell furnaces. They reach zero and the furnaces explode. They see the light from the explosion just it happens. But they are 100 million miles out by then. The light would have taken over 8 minutes, about as long as light from the sun takes to reach earth, to reach the ship.
Factual error: When the boy is crying because he's made to ride a pony, the Texas flag is made wrong. The top star point is toward the red stripe instead of the white strip as it should be. In other scenes the flag is flown upside down - the white stripe should be on top.
Factual error: When speaking to a member of the the Royal Family in Siam (modern day Thailand), one have to speak "rachasap" or Royal Thai. The movie depicts characters speaking colloquial Thai to the King.
Factual error: The Welsh Guards parading at the start of the film weren't formed until 1915. The film is set in 1872.