– Pro Tools 7.4 is compatible with Mac OS X 10.4.9, not 10.4.10, 10.4.11 or 10.5.x
– Pro Tools 7.4 is not compatible with Media Station|PT 1.8.2, which should be uninstalled before updating to Pro Tools 7.4. A new, Pro Tools 7.4 compatible version of Media Station|PT will be available soon.
Pro Tools compatibility information
MediaStation compatibility information