Apologies for deja vue, I originally posted this in Routers and Firwalls but to no avail. Hopefully a more focussed forum will provide a solution. After further fiddling with settings I have more information which might lead to a solution. I have added this at the end.

We have a 3 node network, A, B & C with IPsec Tunnel VPNs connecting each. A & B are in UK and have 2860's, C is in France, Dynamic IP and has a 2830. A & C have now been upgraded to FTTP. B is FTTC ( as good as it can get for the present). A now has Zen supplied Fritzbox 7530 and C has an Orange supplied Livebox 5(not pro).

Initially, both VPNs to C dropped but reversing C (Client = B, Server = C) has got that leg running but I cannot get the A-C route to run. I get a "DOUBLE free for 8234764c: 7a99 from this.id.name3" error when I force dial.

So far I have concluded that the Livebox is limited to a VPN Server unless you pay for the "pro" upgrade. The Fritzbox will support server and client . However, that points to a C to B route working but it doesn't. I tried port forwarding 500 & 4500 UDP on the Fritbox but that didn't help.

New.
I added port forwarding of 500 & 4500 to the Livebox but that didn't help either.
As I workaround, I decided to configure an A to C route by adding A's subnet to C's Profile Index-2 and vice versabut something, presumably the Fritzbox is stopping that from working.

Do you actually have *real* public IP's on the lines that have been upgraded, or do they go via a CG-NAT (100.x or 101.x addresses forget which)