Then that's why it doesn't work, as it's probably not a Universal Binary.
You need to register at Spectrasonics.net and download an up to date version (
always do this when you buy software, check if there's a more recent version first.)
You don't need to authorise, you just need to register your account and serial number, and that will give you the update. Run the update installer (actually, there will be a couple of installers to do as you need to download the library updates as well), then it should show up in Logic and let you authorise, and then use it.