Domain not responding

I am attempting to setup a VPN connection (the tunnel has been successfully created) but I am running into some problems when adding the computers at our satellite location to the domain. I receive the window to input my credentials and after doing so I wait. Finally a error message pops up stating:
“The following error occurred attempting to connect to the domain _____.” “The specified network name is no longer available.”
The network name exists and is being used at our main location. Is there a firewall I need to check or some other suggestion to get past this road block?
Any help will be useful!
Thanks in advance.