Error 29155.Identity source discovery

Hello

I'm installing vCenter 5.1U at the DR site and my AD and everything else is at HQ, We are using VPN to connect the two for what will be SRM.

I have successfully setup SRM in the LAB  via LAN.

While installing vCenter 5.1U SSO on the DR site, I'm getting the "Error 29155.Identity source discovery" I'm not a network guy, but is there a port that is being blocked on my firewall that cause this? is there any blogs on setting up SRM via VPN that you guys can point me to?

Thanks

Bud