No connection with local network after VPN connection established

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http://serverfault.com – If got 4 servers. 2 servers on location BOZ en 2 servers on location RSD. These locations both have connection to another network. Each location has 1 server called VPN-"location" and 1 server DC-"location". When there is no VPN established between VPN-RSD and VPN-BOZ, VPN-BOZ and DC-BOZ can ping each other on hostname and IP-adres. On the moment I establish a VPN connection, VPN-BOZ loses all connectivity to the local network and with DC-BOZ. Though I'm able to connect to remote resources on the RSD-network. VPN-BOZ and VPN-RSD both have 2 NIC's. One NIC is connected to the local network a (HowTos)