This happens if Enjoyable is refused access to your input devices by Mac OS X. This usually happens if another application has requested exclusive access to them. Try quitting any other applications using your input devices. If that doesn't work, try disconnecting and reconnecting the device, then restarting Enjoyable. If it still doesn't work you may need to reboot.
Make sure it matches the name of the application exactly. If you still have trouble, name the mapping @Application and switch back to have Enjoyable try to deduce the correct name automatically.
For reasons yet to be determined, Enjoyable can freeze if it receives its own simulated mouse events. All other applications should work fine; however, mouse events are finicky and it's possible some applications may not like the way they are handled. If you find an appliation that has problems with Enjoyable's mouse support please file a ticket in the issue tracker.