If you keep getting messages that Symphonic Choirs is not installed properly on a Mac, try the following:

You will need to re-enter your serial number and use your authorization key again if you do this, so make sure they're handy.
Find these plist files:

Mac HD:Library:Preferences:Symphonic Choirs.plist
Mac HD:Users:[your user name]:Library:Preferences:Symphonic Choirs.plist
Mac HD:Users:[your user name]:Library:Preferences:com.native-instruments.Symphonic Choirs.plist

Delete the choirs folder, then delete the above plist files, empty the trash, and do an easy install.

If this doesn't fix your problem, please contact Technical Support.