I tried it with another PC, and still the same. I didn't want to try to connect with another PLC.
Continued to do some research, and started by checking the accessible nodes, where I was able to see the safety PLC. Shown here as SIMATIC 300.
Properties as shown here
I don't know how it does this, because it currently doesn't have an ethernet connection. Something to do with the routing?
So I turned the PLC off. Installed the ethernet card, and powered it up. The PLC goes into stop mode.
In the hardware configuration I inserted the new card into slot 7 of the main rack (which matches the physical configuration)and set up MAC address, IP address, gateway etc.
Did save and compile ok, then clicked download. Was offered a choice of accessible nodes to download to, and chose the one based on the properties I initially found.
It did a few things and then gave me this message about online and offline not matching. I know that the information shown here is garbage. Nowhere in any configuration, or physically, does the online module shown exist.
Clicked ok, and it proceeds as if it's going to download, before getting an error message.
The details of which are.
This is deeper than I ever expected to delve into a Siemens (or any) PLC.