Error 633

he extrnal dialup modem (us-robotics)didnot connet to the internet and gives the error message as under.

Opening port…
Error 633. The modem (or other connecting device) is already in use or is not configured properly.

when i uninstall the com port and restart the computer then it works only for one time. I mean that it is must to uninstall the com port and restart the computer before connecting to the internet every time.
please send me the solution

thanks