Continuity mistake: When Anastasia returns home with the contract in her hand, she enters her flat and the computer guy is just finishing fixing her laptop. During this scene her brown leather jacket disappears, but she is still holding the contract in her hand - this is a continuous scene with no time for her to remove the jacket.
Factual error: When Ana is talking to Christian on her cell at the bar and he hangs up on her, you hear a dial tone. A dial tone wouldn't be heard once a cellular call disconnects. Dial tones are only heard on land line phones. Both were on their cells.
Continuity mistake: When Ana has her first Red Room experience and Christian is unlocking the door, her hands are behind her body. As we see Christian insert and turn his key, her hands are in front of her and then behind when we see them both, and then finally in front of her again and they stay that way until they walk in. There was no time for her to change positions since you can see her in every shot.
Continuity mistake: In the business meeting scene, Ana's hair hangs lose at her shoulders. There is a close up of Ana biting her lip with her and her hair is over just one shoulder. In the next shot her hair is back loose. She then proceeds to pull her hair round over one shoulder.
Continuity mistake: Ana is using a PC when she is answering Christian's email on her bed, but he gave her a Mac.
Continuity mistake: When Christian and Ana have sex for the first time, there's one point where he takes her shirt off completely. Ana's shirt is short-sleeved with ruffle-like sleeves, but the shirt that Christian takes off looks long-sleeved, at least when he lifts it above her head.
Other mistake: The first time they have sex, the camera pans up at the end to their reflection which is actually upside down from what it should be.
Continuity mistake: At the end of the movie just before the belt incident scene, Ana walks over to the staircase and crosses her arms. The camera angle changes to face her and you can tell her arms are down by her side. This is evident by the fact that her sleeves don't appear to be "pressed down" or wrinkled but when we see her arms from the facing angle, they look the way they would with added weight. Added to that, if you look at Christian in the background, you can see him lift his head. Once the camera angle changes, you see him do the same motion again.