Maybe it got stuck on a bad image or something...
Try logging into the admin web page, going to Files & Media -> Screensaver
Are you running the Flickr script ? The default path for the Flickr images is '/home/public/data/pictures/flickr/'
if you are, disable flickr, check the path, and re-enable, maybe click remove too to clear out the images
When you moved the files, did you do them as root ? maybe the script is running as the linuxmce user and cannot read the pictures
check the user / perms on the dir that the screensaver is set to