Quote:I've got no error log's.
Just to be sure, you mean there are no errors or oyu cannot access theme. I think on 1&1 they are "hidden" somewhere on their webspace administration.
Are these images by chance taken by different cameras? Sometimes corrupt metadata (exif) causes this as well somehow.
Also, the images per se might not be too big but if you got lots of theme to process thumbs the server could time out.