Hi, can you please try the following:
1. Quite Garageband
2. Make sure Finder is the active application.
3. While holding the Option key, click on the Go menu at the top of your screen and select Library.
4. Delete the following files from your User Library, if they are present:
~/Library/Caches/com.apple.audiounits.cache
~/Library/Caches/AudioUnitCache/com.apple.audiounits.cache
~/Library/Caches/AudioUnitCache/com.apple.audiounits.sandboxed.cache
~/Library/Preferencescom.apple.audio.InfoHelper.plist
6. Relaunch Garageband. It should re-scan for your plug-ins.
