Dialing from a Windows XP machine to a Windows XP machine, dialing into the site (which is set up to accept incoming connections), we can connect and everything is fine during the session.
Modem: Agere Systems PCI-SV92PP Soft Modem
After disconnecting, we dial in again and the computer accepts the connection, but at this point, we see in outgoing dial connection is stuck in "disconnecting" mode. This connection cannot be deleted but it can be renamed, after which a new connection can be created, which has the same problem. (Both connections end up being "disconnecting.")
Rebooting the computer solves the problem, until the remote computer dials out, after which when I connect, I see that the modem state is "disconnecting."
I have not yet tried to reinstall the driver, which would be problematic to do remotely. I'm hoping there's a setting somewhere that can be changed.