Cisco Switching/Routing :: Catalyst 2960S / Multicast Not Working Between Two Data-centers?

Multicast is not working between our two datacenter, we have catalyst 2960S (two stacked) as the internal lan switch, and catalyst 3560E as the external switch, same configuration for both datacenters.The two sites are connected using metro, the external switch (3560) is doing qinq and encapsulate the data from the internal switch with the metro vlan (611).
 
IGMP snooping is disabled for all switches, although we prefer to enable it for the internal switches.For each datacenter there is a different firewall which also act as the router, we are using fortigate as the firewall.Following is the important configuration section:
 
Port 43 in the internal switch is connected to the external switch (both sites):
 
interface GigabitEthernet1/0/43 
switchport mode trunk
 load-interval 30 
 
Port 3 in the external switch connected to the internal switch (both sites):
 
interface GigabitEthernet0/3 
switchport access vlan 611
 switchport mode dot1q-tunnel 
no cdp enable
 no cdp tlv server-location
 no cdp tlv app
 
 Port 8 on the external switch connected to the metro link (both sites) vlan 350 is the internet and 611 is the metro:
 
interface GigabitEthernet0/8
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 350,611
 switchport mode trunk  

vlan 611 on external switch:
 
interface Vlan611 
ip address 192.168.168.2 255.255.255.0
 no ip route-cache 
no ip mroute-cache