As I am using the same pathfinding code in my sidescroller game I hope to find the cause for the error some time soon but I didn't have much time for Gamestudio the last couple of weeks.
Until then it's fine to use just a single region and path for your enemies and objects.
The advantage of multiple regions and corresponding paths is not only ease of usability (in terms of level creation) and performance but the movement in non-regions is more flexible and smoother because the entity will not try to follow a path but move directly to the (potentially dynamic) target.