If the Addon Manager says the scenery is active, which is of course what it saying if you checked the "About", but even without checking, it's clear the scenery is active, because it doesn't let you buy it again, then you can be 100% sure IT IS active, and you don't have a registration, activation, purchase problem or anything related to that.
It might be that:
- You have not INSTALLED the scenery. If you uninstall the scenery, the registriation will NOT be lost so, it will be shown as active even if it's not installed. So, you need to install the scenery in this case.
- You might have an older version of the scenery. Older version of the scenery will never work with the current version of the Addon Manager, and will never work with current versions of AES. So, you need to download the current installer from here.
- You might have another scenery for the area in conflict. We can't help you much with this, if you have another scenery, you need to uninstall it, if it comes with a proper uninstaller, or manually remove all files that belongs to that scenery
- You might have a duplicate AFCAD for Zurich, they usually come with traffic packages, use AFCAD or another scanning utility to find if you have duplicate AFCAD for Zurich.