Or (this is how it is on my 3550) use the 'no switchport' command first. The interfaces default to switchport mode so you can't apply an IP address or other layer 3 commands.

How in the blazing f*£& do I change the static IP address of a Cisco SG350-10 ... I've tried SSHing in and running "configure" then "interface vlan 1" then "ip address 192.168.0.7 255.255.255.0 ...