Internet connection sharing cannot be enabled.
The LAN connection selected on the private network has more than one IP address configured. Reconfigure the LAN
connection with a single IP address before enabling Internet connection sharing.
In your dial up connection, check to make sure you did not specify any IP address for yourself..
If the your dial up connection is still listed as "obtain an IP address automatically", then you are fine.. Next thing
to look for are any applications that could be causing issues (eg: procom, fax software, etc..)... Locate any
processes, stop them, and try again..
Still having issues.. reboot and try again...
If this persists.. you might want to try uninstalling dialup networking (and maybe the modem/drivers) and reinstall
dial up networking..
Odd error, usually caused by another piece of software interfering with your connection.