The port is already open.

This is another very common error message associated with the modem.

In most cases this is caused by another piece of software/program using the modem. Find this program and close it. Most usual culprits are fax software, supervoice, any other voice answering software, or you were using another ISP's internet connection, ie the AOL dialer, etc..

If you were also playing with the init strings for the modem to, this could be the cause, reboot the computer and try again, if you still have the same issue change the init string to AT&F or AT&F1 or ATZ and give it a shot.

Like usual you could try uninstalling/reinstalling the modem and/or dial up networking.