Hi
I got the same thing with 3CX 5.1 i have also tried installing 3CX v6 Beta, i get i different message which amounts to the same thing.
Could not contact License Key Server, makes a bit more sense.
I have discovered since then that this is because i am behind a large Firewall and Proxy Server, PHP is not configured by default to work with a proxy.
I found the information below in a PHP Article for (PHP.ini) it might help you, but i could not get it to work in my environment.
I have asked for changes to our Corporate Firewall, this might take a while.
[Verisign Payflow Pro]
pfpro.defaulthost = "test.signio.com" ; default Signio server
pfpro.defaultport = 443 ; default port to connect to
pfpro.defaulttimeout = 30 ; default timeout in seconds
; pfpro.proxyaddress = ; default proxy IP address (if required)
; pfpro.proxyport = ; default proxy port
; pfpro.proxylogon = ; default proxy logon
; pfpro.proxypassword = ; default proxy password