sorry I sent you a wrong screenshot.
But in the mean time I made some test and I discover that the problem is that I am not using 2 zeroshell box but in one side I am using a dedicate server with a single IP even with 2 vpns bonded.
So I have now to order a multi ip from my provider before give up!
I will keep you informed, but I am still interested in your configuration (if is really working)
Many thanks for now