One thing to have in mind is the location where you run the commands.
Typically (although not mandatory), you run your ncs-netsim create/add commands inside your runtime dir. This manipulates the netsim subdir under the current location.
In this case, I see that you're running the command from within a directory called netsim. If that netsim directory was created in the way mentioned above, then you need to run the add command one level higher (be that the runtime dir or any other dir).
I'd suggest that you delete the netsim directory that you have at the moment, and then retry creating it.
You can retrieve the commands you used in order to create your original setup by checking the content of the file netsim/README.netsim.
The file will list the actual commands you ran in order to create your netsim setup.
