From the GeeThree website, www.geethree.com OS 9.0.4 Compatibility: We have found a problem with Mac OS 9.0.4 and LocalTalk with the Stealth Serial Port extension 1.0.2. Version 1.0.3 of the Stealth Serial Port Extension is now available. It fixes the problem with LocalTalk on Mac OS 9.0.4. It works fine for earlier versions of Mac OS, but is not required. Download this extension and place it in your Extensions Folder. Make sure that any earlier version of the Stealth extension is removed. Reboot system and LocalTalk will now be accessible in the AppleTalk Control Panel.