Hi Marco,
on my blog page (as well as in the posts itselves) that error message appears above the featured image any time I use too small images…
I have set the basic width of any featured image in my posts to 1200×800, so the error appears after using images which are smaller. As soon as I use larger images, the error disappears!
Hope that can probably help you!?
Sven
Hi Sven, because on pages 4 and 5 of your site I see this error again?
See: http://sven-koeck.de/blog/page/4