Player [number] is null, no info

What does it mean when, clicking on the name of a player who has gone offline, PlayerAdministration shows "Player [number] is null, no info" and all action buttons are disabled?

Thanks.

I've had this... and as far as i can tell.. they are offline.. and their player character's body is dead... so therefore.. they dont exist anymore.. till they come back online

generally plugins look at awake or sleeping players only