JPEG attached

Some of my students are having a few problems with Sketchup and I am wondering if anybody here is able to help them. They have created a 32x32cm wallpaper design in Photoshop and need to wallpaper the walls of the rooms they have made in Sketchup with this JPG image. The majority of the class have achieved this with no problems but some students have found that Sketchup puts a gap between each repeat - see attached screenshot. Does anyone know why this is happening?! Any help would be much appreciated.