Avast! blocks VPN connection in Mac OS environments.
[VPN]
When connecting from the Mac OS on which "Avast! Mac Security"
(an antivirus software) is running to the VPN server of the ADC
data analysis system, the connection may not be made correctly
and may return to the initial state where the message
"Ready to connect" is displayed.
In this case, uncheck "Scan secured connections"
in "Preferences > Shields > Web Shield > Settings" in the "Avast!".