Problem with Japanese Airports Vol 3 update

Hi, After downloading and installing the update for Japanese Airports Vol 3,not only does it not work but when opening flight simulator i get this message:- You do not have permission to install new files on this computer.Please have an administrator log on to complete the scenery installation I get this even though i am logged on as an administrator and have never had a problem with any other program. I click OK then get this message :- Unable to write cache file Addon ScenerySimmmerskyRJAAScenery.dat.You log on as auser with write permission. Then i get put back to the desktop. It is obviously related to the JA 3 update because it did not happen before. Anyone have any idea what would cause this and how to fix it? Thanks for any help i can get, Simon.