Slideshow image sizes

Chiller

Not sure if there is something wrong, and I have not changed any settings in my slideshow, but it seems to be grabbing different size images (ie large and medium) from the gallery. I noticed this tonight, when I went to update the photos and there seems to be a black space down the right side of the frame. Is there a quick fix for this? :dunno It was fine last time I checked.
http://chiller.smugmug.com/

Thanks for your help.