Step 5 - check for sharing permissions on which user/groups have access to the files/folders and subfolders.
All files and folders in my Apple Loops directory show root as owner and admin as the group.
drwxrwxr-x 4 root admin 136 Jun 10 19:06 Apple Loops
drwxrwxr-x 35 root admin 1190 Jun 10 16:24 Apple
drwxrwxr-x 15 root admin 510 May 11 2007 iLife Sound Effects
drwxrwxr-x 29 root admin 986 May 11 2007 Foley
-rw-rw-r-- 1 root admin 407697 May 11 2007 Footsteps.caf
https://discussions.apple.com/thread/7687629
1. Go into your "StartUpDrive/Library/Audio" Folder
2. Highlight "Apple Loops" folder, and Press "Command I" (Get Info Window pops up)
3. Go down to where is says Sharing & Permissions (open small arrow on left if it's not already open)
4. Click on the Lock at the bottom right, and put in your Username and Admin password in the pop up window.
5. Look at what's there. You should have an "admin - Read & Write" there. If not then that is the problem.
In my case I had...
System - Read & Write
Wheel - Read only (This was the problem on my computer)
everyone - Read only
6. If you don't have "Admin - Read & Write" then Press on the + button on the bottom left hand side, and choose Administrators.
7. When the "Admin" shows up under name column, change the privilege to Read & Write under Privilege column.
8. Make sure the "Admin" rowis selected, then Press on the Star pop-up menu next to the + - boxes, and choose "Apply to enclosed items..."
9. Press on the Lock at the bottom right to lock it again.