Existing users, 
Remember to install ARD 3.0 onto a machine *before* you upgrade the client to 3.1. Since ARD 3.1 is an updater and you need ARD 3.0 to be installed first, a machine which has already had the client updated to 3.1 will be difficult to set up as a new admin machine.
But not impossible.
Look inside the ARD 3.0 installer bundle, into Contents > Installers. Install RemoteDesktopAdmin.pkg and RemoteDesktopRMDB.pkg, but skip the RemoteDesktopClient.mpkg (that's the one that's causing the failure).
Then install ARD 3.1 update.
Apple Remote Desktop Admin
Remote control to manage Macs.
Version: 3.3
