If you try to reset the modem in the TelePort control panel, you get a warning alert stating:
"The current port is busy and cannot be opened. Quit any open communication application, or turn off AppleTalk in the Chooser (if the modem is connected to the Printer port), and then reopen the TelePort control panel."
Extensive testing indicates that the situation can be reproduced simply by restarting the computer while the network is set to anything besides AppleTalk active in the Chooser, and LocalTalk as the network in the Network control panel.
Solution
The "Busy Serial Port" issue is a software problem. Not a hardware problem. Global Village has provided Apple with an update, GlobalFax 2.5.2P Update, which will correct the problem.
Install the update following these steps:
2. Double-click on the Performa GlobalFax 2.5.2 Update icon.
3. Click the Update button and watch for an update confirmation window.
4. Restart the computer.