The most common error is to have the telephone line in the wrong jack on the modem, or the modem is turned off. The PPP connect process doesn't complete. If your modem is working but you cannnot connect to the server, try the following suggestions. Make sure you are using the correct modem init string for your modem, and that the script came from the manufacturer of your modem. I cannot maintain the connection.
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. University dial-ups disconnect automatically after two hours during business hours. You may have noisy phone lines.