If you use an Emagic USB MIDI interface with an Emagic MIDI driver that's older than version 1.5, you will get the following alert message when you open Logic Pro or Logic Express 7:
"You have an old Emagic USB MIDI Driver version installed. This can cause unreliable MIDI communication and crashes. Please install version 1.5 or higher. You can find the current version on www.emagic.de."
You can download the latest Emagic USB driver here.