My modem is not listed in the Modem control panel. The modem script for your modem might not be properly installed. Your modem may be of a newer variety than the script supports, visit the manufacturer's website to download the latest script. Connect with a terminal program such as Zterm to verify this. Make sure you are using the correct modem script for your modem, and that the script came from Apple or the manufacturer of your modem.
Servers sometimes develop problems that log users out without explanation.
Try calling back later. If you have call waiting, an incoming call can interrupt the connection. Our servers disconnect automatically after two hours during business hours. Some combinations of modems work better than others. Your modem may not be a good match for the modem of the server you are calling.