Error Warning: file_put_contents(private:///.htaccess)

[araitz]

Hola, en mi instalación de drupal me sale este error:

Warning: file_put_contents(private:///.htaccess) [function.file-put-contents]: failed to open stream: "DrupalPrivateStreamWrapper::stream_open" call failed in file_create_htaccess() (line 494 of /home/www/public_html/includes/file.inc).

Y este:
File system Writable (public download method)
The directory sites/default/private/files does not exist. You may need to set the correct directory at the file system settings page or change the current directory's permissions so that it is writable.

Me imagino que están relacionados, no? He intentado subir los archivos que tengo de la template a ese directorio, pero no me deja. Qué permisos le tengo que dar?

Muchas gracias.