I've Read all the post I could find and saw this question asked but not answered. I made my level and put Arokh in. The level runs fine, Rynn can walk around, but she cannot mount Arokh. She also cannot do any damage to him. I haven't seen a SP level with Dragons yet to look at for clues.
Single or MP?
clan : this one is sp.
I just plop him down on the landscape...under view options i have bounding turned on and set to "box" so i can how much space he takes up so that I dont place him clipping through something. I also make sure the level properties has the flight ceiling set high enough for him to be there. Because I usually build my ground floor at 200,000 and the default flight ceiling is 45,000 so that obviously cant work. Other than that stuff I cant think of anything else. I just tried it for testing by throwing a rynn and dragon into a mp map and tried it in SP...works fine.
maybe for some reason you have the dragon placed up really high or below the landscape...if you cant figure it out send me the map and i'll take a look when i get a minute.