In the library, when you first see "the Grey lady", Ray says "That's her! Elenor Twitty - The Grey lady!", seeming to already know what her name was when she was alive. But later, when the Ghostbusters are in the basement, Winston reports that a librarian named Elenor Twitty was killed in the 1920s. Ray says "The Grey lady?", to which Egon replies, "That would be my guess.", implying that this is the first time the Ghostbusters have heard the Grey lady's real name.
Whenever Egon introduces a new pack upgrade, the additional hardware just suddenly appears on the pack. It's particularly noticeable with the introduction of the slime blower, with a green tube running along the cable from the pack to the hand unit that wasn't there mere seconds before. (PC/PS3/Xbox 360 version)
In the PC/PS3/Xbox 360 version, after defeating Pappy Sargassi, Egon takes Peter's radio to talk to Winston, but subsequent shots show it still clipped to Peter's pack strap.
Throughout the game, the Rookie's hair changes between various shades of brown and blond.
The object called 'Galiano's Enchanted Pail' is a toolbox, not a pail.
When listening to messages on the answering machine back in the firehouse, if only one message remains on the machine it will say "You have one new messages." However, this is not so surprising, especially considering that it is 1991 technology. In those days, the extra circuitry required to eliminate that minor grammatical error in an answering machine may have substantially increased the unit's cost, and so been deemed unnecessary by the manufacturer.
The so-called "Grey lady" has been bright purple every time she has been seen. Why would she be dubbed "the Grey lady"? Because "grey lady" is a common paranormalist term for an elderly female ghost, regardless of the coloration of the apparition.
The recording near the Union uniform display at the museum has bad grammar.
Winston states that he hears wings before the gargoyles become active.
When the receptionist informs the Ghostbusters that there is news on the radio, one of them flips a switch on the 2-way radio rather than turning on the car radio.
The Ghostbusters' car is always shown with the lights on and the engine running when in the garage. Since the garage is enclosed, this should be hazardous to their health.
Hoses on the Ghostbusters' proton packs lead to the slime blowers. They always show slime flowing even if the slime blowers aren't being used.
The second time the Ghostbusters visit the Sedgwick Hotel, there are gas generators running (which is a bad idea because of the fumes), and there are lights on, despite there being no one inside.
When driving to Times Square, Ray remarks on how nice it was "after urban renewal". The urban renewal didn't even start until Rudy Giuliani became mayor in 1994, three years after the game takes place. (PC/PS3/X360 version only.)
The game takes place in 1991, yet the World Trade Center towers are not present in the skyline of downtown Manhattan in the game's opening cinematic. (PC/PS3/X360 version only)
Even though you can play as a female rookie in the PS2/Wii version, all pronouns and nicknames remain masculine.