633 - The port is already in use or is not configured for Remote Access dialout.

This error is caused by the modem, when it is in use by another application.

FIX:

Check that you are not running any Fax, Remote Access, Palm or Handheld software that is monitoring or using the Modem. 

The best way to do this is to look at the icons beside your clock in the bottom right of the screen and look for any applications you may have installed.

Once located open the software and disable it from monitoring the Modem or Com Ports, or close down the application when you wish to access the Internet.