Audio problem: When the rowers in the Roman galley were going normal speed, you could tell that the drum was sounding before the drummer hit it.
Continuity mistake: At the end of the chariot race, a heavily bloodsoaked Messala is taken to receive medical treatment. While something is done to his legs out of shot (amputation, presumably) an orderly in a clean white tunic leans his whole body weight on Messala to hold him down on the bed as he writhes in agony. When the orderly stands up, we see that his tunic is still spotlessly white.
Continuity mistake: Right before the chariot race, Sheik Ilderim is on Judah's left side, pointing out the spikes on Messala's wheels. There's a shot of the wheels and then back to Judah, where the Sheik is now on Judah's right side. Judah holds the Sheik's forearm as the fanfare starts. Then a long shot, showing the Sheik, now on Judah's left side again, and Judah removing his hand from the Sheik's forearm.
Continuity mistake: When the baskets are being loaded to be lowered into the Valley of the Lepers, someone loads two heads of lettuce onto a basket. Just as the basket is being lowered, someone else throws in three more heads. When the basket hits the bottom, there are only three heads of lettuce.
Continuity mistake: At the very end, the scaffold that was used to erect the crosses vanishes between shots.
Continuity mistake: Ben Hur's horses change position. When the chariots are preparing for the race and at the starting line, the horse with the pink nose is third from the left, but at the end of the race, the pink-nosed horse is fourth from the right.
Factual error: In the movie, Pontius Pilate is appointed to be governor of Judea around AD 32 (Judah is enslaved in AD 28, spends 3 years as a slave and then at least one year with Arrius before he meets Pilate, who is still not appointed). In reality, Pilate was the governor of Judea from AD 26-36.
Revealing mistake: When Judah and Messala hurl their spears into the wooden beam, the projectiles follow very straight paths all the way across the room to their targets, whereas due to gravity they'd really travel curved paths, practically parabolic, requiring a skilled thrower to aim above the target. What's revealed here is that the spears were rigged to slide on thin wires, to assure that they'd hit the target on cue.
Continuity mistake: In the parade of chariots before the race, the riders are shown circling the track once before making their way to the starting line. As they emerge from the stables, the horses and chariots leave very noticeable tracks on the ground so you can trace their progress around the track. The riders head down the right side of the track (from the perspective of the stables) then make the wide turn to head down the backstretch, and then make the wide turn back onto the right side of the track where they started. The film then cuts to a wide shot of the riders heading back down the right side of the track for the second time, but the track ahead of them and all the way down the backstretch is now clean of any tracks. It's clear this shot comes from when the riders first emerged from the stables. The riders then stop on the starting line on the backstretch, which means they were either transported to the other side of the track without making a third turn, or they did 1 lap around the track in the space of 1 and a half laps.
Factual error: Before the spectacular chariot race, we have the "Parade of the Charioteers." Around the arena you see classical statues. They are just props, they do not influence the storyline at all, they are just dotted around the set to remind us that we are in the Roman Empire. All the statues are just plain white stone. Archaeological research shows that the great Greek and Roman sculptors always painted their sculptures. Skin, clothes, eyes, hair, were all carefully painted to make the statues look 100% lifelike. In the next thousand years the paint wore away, and now, when you go to a museum and look at Greek and Roman sculptures you only see plain stone figures. Yet in ancient Greece and Rome all those statues were elaborately painted. This error applies not just to Ben Hur but probably every classical epic film ever made.
Continuity mistake: During the crucifixion, look at Jesus' hands, there are three clear shots of this. In the first shot you plainly see his blood from his hands on the cross. In the second shot, the blood is gone from the cross. In the third shot, it's back.