After moving a typo3 instance (7.6.10) to a new server, all images were suddenly missing and in the backend in “Filelist” I was told that I had no permission to access the folder. Somehow, “is online?” was set to 0 in the process of moving the files and so the solution is this: Clicking the root node in “list view”, edit File-Storage “Fileadmin” and set “is online?” back to 1.