This can sometimes happen if the MSI.DAT file is at the root level of the Macintosh HD (right inside your main OS drive). To fix this, move the MSI.DAT to any other location, like the Applications folder or another hard drive. You'll need to "re-alias" the MSI.DAT file and place a new alias in three locations.

1. To make a new alias, single-click MSI.DAT in its new location and choose MAKE ALIAS from the Finder's FILE menu.
2. Move the "MSI.DAT Alias" to your desktop and change it's name to "MSI.DAT."
3. Copy this alias to each of the following folders by holding the OPTION key as you drag-and-drop:

Library/Audio/Plug-ins/MAS
Library/Audio/Plug-ns/Components
Libary/Application Support/MOTU/MSI