This is a common problem - little ones who love the idea of a night in a strange bed, until they get tired, and the overwhelming need for familiarity and security takes over. Why not arrange for your visitor to come and stay quite late, playing in the room in which he or she will sleep, and then going home - this will familiarise them with the feeling that the room is familiar at bed time. Next, on the overnight day, introduce a story, or game, which can only be played then your visitor is actually in bed - make it a real treat or favourite. If you time it right, your little one will be tired enough to drop off in their 'new' bed, but make surte you leave a night light on, and pop in every few minutes to reassure them. Make occasional movements around the house to reassure your visitor that you are still there - maybe turn the telly up a little, or hum as you visit the bathroom. These all build security and should alleviate the distress - eventually. Good luck!