Featured Images broken after migration

Dear all

I am really desperate. I already migrated my WordPress page several times but this time I have a problem that I just can’t solve.

After the last migration everything works fine on the new server apart of the featured images and thumbnails of some posts.

Something is very strange, even on the old server:
For example there is this picture on the old server. You can open it:
http://preview-web01.113546.aweb.preview-site.ch/wp-content/uploads/2015/03/proto_nemesis_1473_a_1142.jpg

When I login to the FTP server and browse to the directory 2015/03/ there is no such picture! It is just not there physically. I already double checked with the old service provider. How is it possible that the image is shown in the browser while it is not existing on the FTP server?

On the new server the image link, FTP content and database are exactly the same as on the old server. But when I try to open the same file on the new server an 404 error page is shown:
http://rcworld.ch/wp-content/uploads/2015/03/proto_nemesis_1473_a_1142.jpg

On both, the old and new server, I can find the original image here:
New: http://rcworld.ch/wp-content/uploads/2004/05/proto_nemesis_1473_a_1142.jpg
Old: http://preview-web01.113546.aweb.preview-site.ch/wp-content/uploads/2004/05/proto_nemesis_1473_a_1142.jpg

What can be the problem? How can I make the images work on my new server?

I really hope that there is a genius out there who can help me!

Thanks a lot!

Best regards,
Lorenz