exporting vendor items that are in a billboard?

So im pretty new here (already read the rules and introduced myself) and after watching the import/export video i figured i'd try it out on vendor billboards, you know the common ones that we see everywhere in various shops, where it has a picture of some SL model advertising clothing or some bs like that, and if you click on it you get the option to buy it, and after it gives you a box to open (usually) with the content inside. well i was using dark storm fiddling around with it and i kept trying different ways to copy the items inside the billboard, and i ran into two problems, 1) either i couldn't upload the inventory items at all or 2) i'd get an error message saying i didn't have permission to copy/modify those items, even though i changed the copy/modify settings in the upload panel. anyone what im doing wrong or a work around? Though i did manage to copy items from SL players/store models.