If I remember correctly, this is just the system reacting to seeing a third box attached to the line, as the maximum currently is 2 and it doesn't know one of your boxes will never reconnect (because it is broken).
Usually, you can click on "set up" or similar wording and confirm that this new box is now the main (or master) box and you should be able to continue. You may need to also do this the next time you use the other box, then the system knows these are the 2 boxes in use going forward.
