Well apparently it was a settings problem with Serv-U, but I couldn't fix it.
So instead I updated Serv-U and that cured the problem.
But thanks, anyway.

Hi there In the directory listing of every folder I see the current folder again, preceeded by / . Example: Inside Folder1 I see /Folder1, inside folder / I see /. If I open the folder, I'm in // and then /// and so on. This is a problem with synchronizing, because the folder // doesn't really exist...