Right now IPv6 is enabled by default in Mac OS X and VyprVPN doesn't support IPv6 at all, so when a user doesn't disable IPv6 and surfs the internet over a network that provides an IPv6 address for him then he is basically unprotected and his real IP address is not hidden.

Maybe you should add a warning when someone first launches the app which says that IPv6 is enabled and that it is highly recommended to disable IPv6 and offer him a button to do so, because right now you have to use the Terminal.

Or, even better: add IPv6 support for your service, but there is already a ticket for that in the general section.