Always-On VPN through a Checkpoint FW only one VPN session working

[ham2065]

Hi 

I have a setup with Microsoft Always on VPN AOVPN running through a Checkpoint R80.40 Cluster and terminated on a Microsoft RRAS server.

I have allowed inbound traffic on ports UDP 500 and 4500 and created manual static NATs translating the external IP to the RRAS server in both directions. 

The AOVPN works for 1 vpn client but when a second client tries to connect they get a generic network connection error. 

We have a similar setup at another data centre running through an ASA cluster and AOVPN is working as expected i.e. multiple AOVPN simultaneously.

Is this due to a Nat Traversal issue?

Any help here would be appreciated.