Craig Brooks was originally cast as Brooker, naturally, and had filmed 2/3 of his scenes before deciding that he didn't like film-making and refused to finish. Production was halted for over a month before Paul Michael McIntosh stepped in to re-shoot the character. As a result the continuity towards the end becomes somewhat erratic.
The unusually warm Scottish winter of 2011/2012 meant that there was no snowfall, which the production relied on for atmosphere as well as reflecting light to illuminate the locations.
Although Craig Brooks was re-cast, traces of him can still be observed in the film. His face cannot be seen but he plays the Minder at the fortress gates, his ghostly whistle of 'We Wish You a Merry Christmas' was actually him, not Paul Michael McIntosh, and when Shawn opens the envelope the very brief low angle as he pulls out the photograph is actually of Brooks. The photograph was later re-shot and reproduced when McIntosh was cast but the low angle could not be re-shot as Shawn Elestren had already dyed his blonde hair back to brown.
The cameras used by Shawn Watson to shoot the movie needed massive amounts of light to make anything visible. This caused apparent continuity errors during the scenes set during the twilight hours as the film looks as bright as day when the camera is facing west but dark as night when facing east despite being shot at the exact same time of day.
Tantallon Castle on the east coast of Scotland was used as the location for the fictional Foghollow Fortress. Shawn Watson had to break in three times in order to get the footage he needed. He used less than 10% of what he shot.