Mike-
Can you confirm that the license for Blackhole is activated in your account?
Additionally, is Blackhole located at the following location?
/Library/Audio/Plug-Ins/Components/Blackhole.component
If you can confirm those, then try these steps:
1. Quit Garageband.
2. Remove Blackhole from the following location: /Library/Audio/Plug-Ins/Components/Blackhole.component
3. Relaunch GarageBand and then close it again.
4. Run the Blackhole installer again.
5. Make sure Finder is the active application.
6. While holding the Option key, click on the Go menu at the top of your screen and select Library.
7. Open the Caches folder, click the AudioUnitCache folder, and delete com.apple.audiounits.sandboxed.cache
8. Go back up to the Library folder, click on the Preferences folder, and delete com.apple.audio.InfoHelper.plist
9. Relaunch Garageband. It should re-scan for your plug-ins.
-Tom
