Sondra's date of birth on the form at the US Embassy (14 April 1942) does not match what is shown on the closeup of her passport (3 July 47). The passport is Betty Buckley's actual birthday.
When Walker is on the roof of the apartment building and the suitcase strap breaks dumping its contents, the Statue of Liberty clearly tumbles over the overhang. In the next shot it is on the overhang on the other side.
The level of beer in Walkers bottle in the scene in the bar with the drug dealer changes from nearly full to half between shots.
The match from the matchbook sounds like a wooden match when it falls after Dr. Walker checks his watch with it.
Dr. Walker's beer bottle is foamed to the top as seen over his right shoulder. When the scene changes to look down the bar from his left, the beer has no foam at all.
When the hotel manager grabs a telephone book to call the concierge at his gym, the phone book clearly has a break in the spine at exactly the page he needs, so that it flops open effortlessly.
When Walker is shaving, just after his shower, when his wife vanishes, he is wrapped only in a towel. However, when he walks across the hotel room to answer the doorbell, it can clearly be seen that Harrison Ford is wearing white underwear under the towel.
In the airport scene with Michelle, Walker is terrified that the drug-sniffing dogs will find dope in their suitcase. Michelle assures Walker that there are no drugs, and the dogs walk by calmly. Walker seems to have forgotten that he's carrying at least a gram of cocaine in his pocket, which the police dogs don't notice either.
When Walker meets with the two American officials in the US Embassy, the boom mic can be seen sneaking into view throughout the shot in the over the shoulder shot of the second man, seated at his desk. It is hidden by the man's profile and the knot of his tie, but as he moves back and forth, its silver shape is clearly visible multiple times.