Audio problem: When Tess meets up with her boss toward the end at the helipad, notice that the helicopter engine sound is playing, but the props aren't turning. Helicopters blades always turn if the engines are running, just like an airplane.
Continuity mistake: From Katherine's office there is a beautiful view on a waterway (New Yorkers will know the name). In every scene there there is a lot of discontinuity regarding the ships and ferries appearing and disappearing, especially when Tess comes to the office the second time to take some notes. (00:16:10)
Continuity mistake: When Tess arrives at Cyn's party at the bar, she finds Mick drinking. She joins him and puts her purse on the table. Mick asks her to dance and the next shot you can see purse strap is back on her shoulder. (00:53:40)
Continuity mistake: Tess' hair changes from past her shoulders to shoulder-length during the party and then back again after the party.
Other mistake: When Katherine reserves a room at a hotel she talks German. From her weird diction it's obvious that Sigourney Weaver has somehow memorized the text without actually knowing what she is saying. (00:21:50)
Continuity mistake: Near the end of the movie, in the scene where Tess, Jack, and Mr. Trask exit the elevator that Katherine and others are using, they move to the next elevator to hear Tess' version of how she arrived at the deal. Jack says, "This elevator is open, sir." The shot changes as Jack, Tess, and Mr. Trask go to board this different elevator. The part in Jack's hair is suddenly on the right side of his head, instead of the left side, as in the prior shot. Once in the elevator (just the three of them, now), his hair part is back on his left side. I suspect the film had been reversed.
Plot hole: We see Tess wearing Catherine's clothes when Catherine is gone, but Catherine is much slimmer than Tess. They wouldn't fit without being altered and she had no time to do so.
Continuity mistake: Melanie Griffith has continuing weight gain and loss, throughout the film. Particularly during the drinks scene, when she has short hair, she is slim. The next day in the office (or when she has longer hair) she has a much puffier face. [At the time she had a well-publicized alcoholism problem. The puffiness was when she was drinking most heavily; the thinner scenes were when she was not. That is the explanation, but a mistake nonetheless.]
Continuity mistake: The timing of the ending is all wrong. First, we see Tess at Cyn's engagement party; then, no more than a week or two later is the business meeting where Katherine storms in and "outs" Tess. We then next see Tess at Cyn's wedding, a perfectly planned affair with fitted bridesmaid dresses and everything - implying that some time has passed, since it takes much longer than a few weeks to pull a wedding like that together. This seems to be bolstered by next seeing Tess going back into the office to get her stuff back, and Katherine's broken leg is now out of its cast, and she has a cane. BUT - Tess goes back into the office to get her stuff, which would imply that only a few days at most has passed - who leaves their stuff very long in an office where they've just been fired? Also, she runs into Katherine putting the finishing touches on the deal - it doesn't seem likely that the deal, which was agreed upon in the meeting, would take very long to be finally finished. The business world as depicted in the movie moves very fast.