ISCSI won't pass gateway

We are having a network issue connecting two Open E DSS systems for iscsi replication, there must be something very simple we overlooked :

One system is here, in our 192.168.0.0/24 network. The other is in our datacenter in the 10.211.0.0/22.

First we tried over WAN, on both ends we forwarded 3260 and tried to establish an iscsi connection by entering public addresses, but that did not work.

Now there is also a gateway here and a server there that provide a VPN tunnel. The VPN system is equal to a router that connects two networks. We tried by this to get a connection. The OpenE in our office has its default gateway set to the VPN gateway, and so should find the 10.211 network address over the gateway, but it does not. The OpenE in the datacenter has the default gateway set to the VPN server, the gateway is set to forwards incomming port 443 and 3260 to the OpenE here, by that route the OpenE there should find the one here but it does not.

Every computer here can see the OpenE there, and every computer there can see the OpenE here, but OpenE cannot find OpenE eitherway.
Now is there maybe a port that we do not know of that also has to be forwarded ?
Or is OpenE Iscsi replication just not listening to the systems default gateway ?
What is the usual way to do this anyway ?

With kind regards,

UPservers