this is only for windows 7 users.
If you have imported any custom scenery with rct3 importer and you get a "no svd for sid" error when you open the custom scenery in rct3 And you have place the Scenery imported in your rct3 directory/style/themed from the rct3 importer.The folder of the scenery is not available there because the scenery isn't the rct3 directory it is somehow is in C:\Users\your username\AppData\Local\VirtualStore\Program Files\Roller Coaster Tycoon 3 Platinum\Style\Themed\Style\Themed.Cut paste it in your rct3 directory\style\themed folder.

To fix this, before you open the importer, right click and click "run as administrator" so it has permission to save file in the Program Files directory.