VPN - DNS that uses custom page when domain is unknown

Hello,
my SSL VPN works fine, but I found a particular situation that I cannot solve.

One of remote clients uses a DNS server that redirect to a web page when it's not possible to resolve a domain name. So it happens that when I try to ping my LAN File Server name, its ip address is replaced with the ip of web server (in this case 212.52.82.27, that is the ip of Auto ricerca libero.it).

For the moment, I modified "host" file... in your opinion is there any other "more elegant" solution?

Thanks
eclipse79