Continuity mistake: On the inspector's boat Frank's wrists are handcuffed together with a railing between his arms to secure him in place. There is a very short chain between the cuffs, 4 to 5 inches at most. When he's pulled free by a rope from Elise's boat he starts 'climbing' the rope hand over hand. In one shot his hands are over a foot apart, he's obviously not wearing the handcuffs. When he gets onto Elise's boat his hands are cuffed once again, she shows him how to pick the locks to get the cuffs off.
Factual error: Frank and Elise approaching to Venice by train. Train announcement says "Arrival at train station Santa Lucia in ten minutes". Landscape from the train window is green and hilly. I'm from Venice and no way you find such landscape 10 minutes from Venice Santa Lucia. Most probably you would see a gray Mestre, Venice inland city, or a completely flat and not green land (for at least 30 minutes from/to the train station of Venice).
Other mistake: In the scene where Jolie drops Depp off at the airport she asks him to tie them off. Depp does so with a solid knot. Jolie then unties the knot from the boat side and leaves him behind. The rope should still have been looped around the mooring where Depp attached it, and hanging in the water where she untied. It is completely gone.
Factual error: When Elise drops Frank off at Venice airport, we see the colorful houses of Venice proper quite close in the background. But Venice airport is on the mainland side of the lagoon, quite far from the Venice islands. So the houses would have been much, much further away.
Add timeJacob La Cour
Factual error: When Frank and Elise arrive in Venice, they sail from the train station to a hotel which is also located on the Grand Canal (from the balcony we see the Rialto Bridge). However just after leaving the station, we see Saint Marc's Square from their boat from the other side of the lagoon. That is very far from the station - and not on the way to that hotel.
Add timeJacob La Cour
Deliberate mistake: Elise goes to the "Gare de Lyon" and takes a train that goes to Venice (an italian ATR - AV, a high speed train). The only direct train to Venice is a sleeper train, in addition the travel time (over 8 hours) required would make the use of a high speed implausible. Furthermore these trains are not running in France, "the connecting" railroad is still under costruction.
Factual error: When the two arrive in Venice, they check into the Hotel Danielli, an actual Venezia landmark which sits on the Lagoon, at least half a kilometer down from the Piazza San Marco When Johnny Depp goes to look out the window of their room, he is looking at the Rialto Bridge... a good 20-25 minute walk on a good day.