I have a cable modem set up on USB that is working fine. What I want to do is to connect the same PC through a switch to another PC and printer via the NIC. The issue is that as soon as I make both networks active they stop working. I can disable the USB Internet connection and the LAN works or vice versa. The LAN is on a 10.1.1.x subnet and the USB modem is on a public subnet so I am lost as to why they should interfere with each other. If you look on the Network and Sharing page they both go to Local Only connections. The LAN and Internet are set up on DHCP.

Any hints as to what I have done wrong here?