Are you using the ones from the n900 wallpapers site? Answers are here in this thread. If you are having trouble with the actual application, (i.e. it crashes or won't let you open the 'change brackground at all) then there's a problem with the path on the .desktop file. Edit it using a text editor as follows: becomes Where 'image' is the name of the set. If you can view and access the 'change background' but the set you want appears void, there's an extra 'space' on the end of each line you need to delete - again using a text editor. Hope that helps.