VPN Tracker 6 won't work on Mac OS X Yosemite

Equinux VPN Tracker 6 won't start on Mac OS X Yosemite. When starting up, a message says

Unable to load kernel extension

And invites you to restart, but to no avail.

Needless to say, I don't want to give them € 50 to upgrade to version 8 for the sake of a new UI. And I find their licensing policy (upgrade or perish) very unfriendly.

Any idea on how to get it to run?