Yesterday Sibelius started throwing up a pop-up at launch:
Installation Error
T-RackS 3 TRackS3 Vint Comp 670 has not been properly installed.
Please run the installer again.
Clicking OK then brought up another pop-up
Went looking for a solution and found it here
https://discussions.apple.com/thread/2723619
Go to Folder
/Library/Audio/Plug-Ins/Components
Deleted
Worked!