it's probably DNS related.
you need to check that what the DNS the system is set to use when you bring up the VPN.
For example when I bring up my StrongVPN connection, it's set to use an external DNS so if I want to access a system on my network i need to use the IP address.
Though I can access some SMB shares but I have them mapped at login via group policy but if I wanted connect to my samba file server afterwards, yeah gonna say the server isn't found if I have the system name.