@TheArtfulDodger; just do as the message says; either
- with the Kobo attached click the arrow besides device and select Configure Device; then check the box Attempt to support newer firmware
- with the Kobo not attached click the Preferences button, select Plugins in the Advanced section, expand the Device Interface Plugin selection, select the Kobo Reader Device interface line then hit the customize plugin button. Finally on that screen check the box Attempt to support newer firmware
As I've learnt recently this message will occur for ANY Kobo Device after a current version of Kobo Desktop has been used, regardless of the firmware level on the device.