What to do if the plane button is visible but inactive(grey gets not activated when hoovering over it and you cannot click it?

Re: Range Rings

I loaded the plugin the first time and I was able to define rings that were drawn on the map. I managed somehow to delete the rings on the map, but the defined distances are still in the menu, the red x does not remove the definition, I can only add new distances but they are no more shown on the map. basically this plugin does not work or it is missing some important instructions