Other mistake: Before Becky and Miles go down the steps after leaving his office she says "I've been in Reno". The camera goes totally out of focus for a second right when she says, "Reno" the second time. (00:07:10)
Other mistake: When the Id creature is melting through the door and Morbius is denying he subconsciously created it, the Commander draws his blaster giving the impression he will kill Morbius to save them if necessary. But Robby deactivated the blaster just a few scenes prior. Was he going to beat Morbius to death with it?
Suggested correction: That was a moment of desperation, so he wasn't thinking, and, well, yes anyway.
Other mistake: It supposedly takes three weeks for the space ship to arrive at the 13th moon of Jupiter. Yet the people following their progress back on Earth stay in the same positions and clothing throughout all this time.
Other mistake: As they travail to The Pentagon in Washington, Carol and Dr. Marvin sit in the exact same mock-up of an airplane's interior that we saw earlier in the movie when a UFO passes in front of it. (00:00:45 - 00:27:00)
Other mistake: When the title card is shown, the copyright year is shown as 'MCMXXXIV' (1934). It was released in 1956 (MCMLVI).