If you have a Member Server running RRAS and you try to access the Modem Pool, you may receive:

The modem is being used by another Dial-Up Networking connection or another program. Disconnect the other connection or close the program, and then try again.

You may also find that the Fax and Proxy services do not function.

The workaround is to configure RRAS not to capture the ports in the Modem Pool or to uninstall the Modem Sharing client from the RRAS server.