Hi @Anonymous ,
Did you changed administrator password recently? Or the permission of app pool to the virtual directory? Please check the permission of virtual directory.
Make sure the application pool has full control permission to virtual directory. Or an easier way is to remove the ftp site and application pool and create a new one.
It's very likely that the problem you encountered at first is also caused by this becaused it's also a permission issue.
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Best regards,
Bruce Zhang