If you get an error that the dialer is in use when trying to start a dial session, this means that the system is in use with your login somewhere else.
Check to make sure that all other browser windows are closed and that you don't have a hidden session open behind any browser windows.
Check to make sure you are not sharing an account with someone else logged into your account on another machine.
If you are sure that it is the only window open, click the option to disconnect the active session and restart your dial session. If this does not work, please contact support for assistance.