Do you have the other VPN software installed? Please uninstall that and reboot your system. If you still get this error after rebooting your system, with only BolehVPN installed, follow the steps below.
Open a Terminal window. Type in kextstat
Scroll down the list of results. Look for something like foo.tun and foo.tap, com.cisco.cscotun, com.viscosityvpn.Viscosity.tun and com.viscosityvpn.Viscosity.tap or com.pogoplug.xcetun.
Type in sudo kextunload -b "name of tun or tap found in kextstat"
(For example, if foo.tun or foo.tap are found, type in sudo kextunload -b foo.tun or sudo kextunload -b foo.tap)