Just found the answer at https://www.ads-software.com/support/topic/242976?replies=6
amenthes
writes:
In my case: I changed folder-permissions with my FTP-Program.
After the Update i always got The uploaded file could not be moved to /some/file/path (last part was of course replaced by me) after uploading a file t the gallery.
For some reason i needed to chmod my files to 777 to make uploads work again.
