Lost VPN connection between a couple of our sites

[ScottyB87]

Hi,
I've got an issue that's really left me scratching my head.

Over the weekend one of our sites (Remote 1 on the below picture) lost connection to our CoLo data centre.
All the other sites are fine (except one that I'm not too concerned about, also noted on the picture)
I say 'lost' connection, the VPN claims to be up, and when I ping from either end, whilst pings fail, I do see ICMP traffic when doing a packet capture from each end.
I guess it must be a routing issue, but I just can't find where to look.
Both firewalls are running 2.7.
I can post any logs if it would be helpful, but I'm hoping the good people here will be able to help me and stop me from decending further into madness!

Thank You!

[ScottyB87]

So additionally I've disabled the OpenVPN and recreated the tunnel using IPSec and it's still having the same issue..