Factual error: Robert's voyeuristic neighbors are using the same elevator as Robert does and tease him about seeing him and Amy through his bedroom window. But if they were able to see into his bedroom, they would not be using that elevator; it would be in another building. From the outside shot of his apartment building, it would be impossible to look into his bedroom.
Other mistake: When Amy runs out of the basement wearing Robert's pants, the pants are at full length, with the belt under her arms and the bottom of the pant legs at her ankles. When she is standing next to Robert, though, it is clear that he would have to pull the pants all the way up to his ribs for the legs to be the right length on him. Also, the pants are unzipped and the zipper pull is hanging just below Amy's breasts. Since a pants zipper is usually just an inch or so above the crotch, Amy would not be able to pull the pants that high unless there was a 12" drop between the zipper and the crotch of the pants.
Factual error: When they are in the bathroom in the bed and breakfast in Vermont, Debrah is complaining that she thinks she's boring and Ray answers that he ran out of things to say on the George Washington Bridge. You wouldn't take the George Washington Bridge from Long Island to Vermont.