Resolution

This can happen if the Audio Unit cache file is unusable. To resolve the issue:

1. In the Finder, choose Go > Go to Folder from the menu.
2. Type ~/Library/Caches in the "Go to the folder" field.
3. Press the Go button
4. Remove the "com.apple.audiounits.cache" file.

The next time you start Logic, the installed Audio Unit plug-ins will be rescanned and Logic should then startup normally.