Hi Karsten,
The images appear to be parsed, but the URL seems to be incorrect. WordPress returns the thumbnail sized URL (150×150), but it does not seem to exist. It might have been deleted, or not created, but still somewhere stored in the database.
For example, one of the images are pointing to: http://haushaltsblogs.de//files/2015/02/abfluss-verstopft-haare-reinigen-150×150.jpg
Try the following change, this should help: http://i.imgur.com/7bqfeTK.png
