Originally Posted by mccormw
The strange thing is that when I try to add books from another directory (I am trying to centralise my eBooks on a NAS server btw) it tells me I have a device connected. I assume that is what it means because the column 'On Device' is now visible, but it is showing Main Memory.
Calibre will tell you what device is connected in the lower left corner. I suspect you connected to a folder using the Connect to Folder