Please, tell us exactly what network you're trying to add. Your SME Server (most likely in serveronly mode) has IP 192.168.1.42. I guess its netmask is 255.255.255.0, and its default gateway is 192.168.1.1. Now, you try to add which network, with which netmask, and which gateway ? From the error you've posted, it looks like you have not used a gateway that SME can't reach (outside of the 192.168.1.0/24 network)