I am trying to configure OVPN behind two NAT Routers and i am missing something.

Here is situation

hAP  <---> INTERNET  <--> Router A: CCR   <--> Router B: CCR  <---> Router C: CCR with OVPN

I have done port mapping and masq on Router A,B and Router C has OVPN servers configuration. VPN connection is established but not even ping is going trough. And directly after timeout is conncetion reseted

For test I have placed hAP between router A and B and VPN is established and ping works fine also there is no time-out reset. So i presume that OVPN server is correctly configured.

Did anyone else played with similar configuration or have some ideas what could I be missing?

maybe thats some medium party to blame ? eg say ISP(of any scale) or authorities ?
for multiple NAT penetration - sadly other things suit better despite flaws. like SSTP and alikes. its pain .. to use, but would Work anyway.
MPLS/VPLS isn't bad option too if you had uplink/ISP supporting/offering that.

more and more Looks like some ISP issue. Interesting is that a have established OpenVPN connection to Linux OpenVPN server that works without problems :S (but is using UDP).

I'll try to play with other ports and compare what is different compare to LinuxOpenVPN server.

Thx anyway a was hoping is not ISP all the time.