The specified network name is no longer available

Are you able to ping by its DNS name or IP address.  If you are not able to ping by DNS, but IP, then you will need to register that computer's host A record in the DNS server in that zone.  It could be another problem.  I will need more information.

When you say map, what exactly do you mean?  Are you talking about mapping a drive to that computer?  Are you using a VPN connection to the headquarters?

Okay Here is the scenario.  Server A is currently in a remote site.  Server A is trying to connect to a Server B(\\ServerB\C$) in the headquarter location.  When we ping Server B we get Server B ip address 111.111.102.102.  When we try to open through windows explorer and place in the address bar \\ServerB\C$ we get the "The specified network name is no longer available".  Server A is part of its own tree in which it belongs to the Server B forest.  In other words it has its own domain controller.  So if we try to connect to another server, this case Server C, which belongs to the tree that Server A is located, we can go ahead and map( i.e. \\Server C\C$\). But when we go out of this tree to any other tree, we get the error aforementioned.