One of the American ghost hunters, who proclaims to never having been to the UK or even to know where Wales is, mentions British TV program "Antiques Roadshow" in a wisecrack. However, there is an American version of "Antiques Roadshow".
In the instances where the gramophone is seen playing a record of "In the Evening By The Moonlight", the needle appears to be playing from the center of the record at the beginning of the song, whereas this would actually be the end. It should be played from the outside in.
When Annie is in her apartment prior to flying to Britain, it's clear her that her apartment is in Britain because the light switches and power sockets are of British design.
In one of the early scenes where the scientists are travelling to the castle, they are actually travelling in the wrong direction on the M4 motorway. One would see signs for Cardiff, not Swansea, when travelling to Margam Park.
It is stated that there is no way out of the castle once the main door slams shut. However, when the team regroups just after hearing Kirk's scream (at 1:00:28; 1:03:00 on the U.S. DVD,) there is clearly a sign in the background pointing to the Fire Exit. By law, Fire Exits in the UK have to be able to be opened from the inside. They should have just followed the signs to escape.