First, verify that the ARIA Player is up to date.
Once the ARIA player is up to date, try the following:
- Navigate to Macintosh HD > Library > Audio > Plug Ins > Components.
- Verify that ARIA Player AU.compenent is in this folder.
- Open Logic and go to Preferences > Audio Units Manager, then click Rescan.
The plug in should now be available under AU Instruments > Garritan.