Not all VNC versions support IPv6.
RealVNC supports IPv6. You must select Prefer On in the RealVNC server settings or IPv6 and VNC will not work with CC-SG.
The TightVNC client will work with CC-SG if the server setting is changed to Prefer On.
Free edition of RealVNC does NOT support IPv6
Personal Edition of RealVNC supports IPv6, but it is a 30 day trial version, and then you must buy a license.
Enterprise edition of RealVNC supports IPv6 when you buy a license.
When adding VNC interfaces for Windows 7, make sure that ICMPv4 and ICMPv6 are allowed by the Windows 7 firewall.