Main Problem is the RouterOS License:
The LHG 5 ac comes with a RouterOS license 3.
This allows Point-to-Point and Point-to-Multipoint as a “Slave”
Point-to-Multipoint requires the “Master” to have a RouterOS license 4.
Solution : Mikrotik offers L4-Licenses for Money =)
More Info under : http://forum.mikrotik.com/t/ptp-v-s-p2mp/145788/1