Plot hole: The aliens' plan ("plan 9") is deeply flawed. The aliens resurrect the dead to make earth people accept the aliens' existence. However when Eros reports to his leader, he says that "none of the risen have been seen." What's the point of raising the dead if they aren't seen anyway? And while later, yes, the old man enters a dwelling and is by everybody, anything before that was just a huge waste of time on the aliens' part, making the first phase of the plan completely senseless.
Factual error: The cemetery is full of bare branches of medium to small 'plants'. Since this is southern California, they should have leaves.
Continuity mistake: As he interviews Col. Edwards, the phone wires hanging off the side of General Roberts' desk move between shots without anyone touching a phone. (00:41:00)
Continuity mistake: In scenes at the general's office, a large wall map of the U.S. is in the background. In some of the closeups you can see that it's a Santa Fe railroad map - and in others the words "Santa Fe" on the logo are taped over. (00:42:05 - 00:45:30)
Revealing mistake: When the people in the military are firing the rockets at the UFOs, you can see the rockets launching from platform are coming from the outside of the platform. (00:19:00)
Continuity mistake: As they look into Tor Johnson's empty tomb, one of the police officers says it looks like (the dirt) has fallen into the grave. In the next shot as he goes into the hole there is no dirt in it. (00:40:00)
Visible crew/equipment: Someone's hand from behind touches the shower curtain in the cockpit of the plane as the pilot says, "You better radio in for landing instructions, Danny". (00:04:15)
Revealing mistake: In the cemetery, you can see the actors' shadows on the fake sky.
Deliberate mistake: In the alien spaceship, Eros speaks of the "Solarminite", Jeff Trent calls it "Solinite" and Col. Edwards calls it "Solar-inite". (01:05:55 - 01:07:50)
