OK this was because the interface was set to DHCP
So we have an IP address, but no web interface.
According to the manual the web interface can be set using the 'web mode' and 'web port' commands using 'show ip interface' but we just get an error when we type 'show ip interface' into our system.
I think we need to get out of the switching part of the interface but we don't know how.. 😞