Is your MacBook behind NAT? You might want to make sure about that, because there is an issue with such setup: http://forum.mikrotik.com/t/ipsec-and-nat-t-problem/30115/1 . I faced it when I was trying to set up IPSec/L2TP VPN on my XP laptop. You must exclude this one before you take any further actions. Also enabling ipsec and l2tp event logging on your mikrotik should give you mode idea of whats happening when you try to connect.