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Hello Gizem, Are you by any chance running Ubuntu Linux through WSL or a VM on a Windows machine - AND/OR  - trying to write your data from Ubuntu linux to a mounted NTFS file system on a Windows machine?   The Windows file system does not support symbolic links and so you need to set SUBJECTS_DIR to point to path on a Linux file system.  I am not aware of linux OS file systems that do not support symbolic links. - R.