Factual error: When Iris is unable to sleep she looks over at Amanda's bedside clock which displays 5:00 pm, however, moments later Iris discovers a button to lower the shade. There is bright sunlight coming into the room, however, in December the sun sets prior to this time (about 4:45pm according to timeanddate.com)
Other mistake: When Amanda's driver brings her to the cottage for the first time, he tells her he can't drive her up there because he would not be able to turn around, but the same driver picks her up at the cottage when she is leaving and presumably has no issue turning around at all, and you can see it's a flat field in front of the cottage.
Factual error: The outside view of Kate Winslet's 'cottage' is not a cottage at all - in England it would be considered a large detached house and it has several rooms on the upper floor. However, the inside depicts an actual cottage: there is only one bedroom (Jude Law has to sleep on the sofa), the bathroom is too small for a regular sized bath, and the downstairs only has a couple of rooms. So the outside view of the house is large, whilst the interior is depicted as tiny.