Gap access Active Directory with VPN tunnel

Hi,

I've make a VPN tunnel with two Fortigate 60D with this video tutorial:

http://video.fortinet.com...-w-overlapping-subnets

The connection VPN is ok and the ping work correctly but I won't to connect some client in the active directory.

When I connect the client to the windows domain it's returned an error; the primary dns on the client is the ip of the server windows domain controller and the ping to this server is ok.

in other if i connect to he server with start-> run -> \\server

and insert the domain credential, I've the access to the server data.

why the active directory not correctly run on vpn?

tnks