Continuity mistake: When they go to find Private Ryan there are eight of them, when they go to a French town and a solider picks up the little girl and he gets killed there are seven, right? Wrong. A few scenes later, the camera shows all eight of them marching on to the next town, only in a far away camera shot so it's hard to see. (01:23:11)
Other mistake: When Will Smith checks into the hotel and his credit cards are invalid, we see that the time is 5:38 and it is daylight outside. The only problem with this is that it is supposed to be around December given all the Christmas decorations. It would be dark then in the Baltimore, not soaked with daylight.
Revealing mistake: In the scene where Captain Love and Antonio Banderas (as Zorro) meet in the hallway of the hacienda, two guards rush down the hallway and drop their rifles and swords. Zorro asks them to bend over and then proceed to kick/nudge them out the window. If you watch carefully, you'll notice that the guard on the right (furthest from Zorro) reacts to the kick too early. (01:33:30)