bouznak,

If you get the "updating desktop entries... Done" message after doing the installation it means it has already been installed. Or do you mean you get this after doing apt-get update? It would be better to post full logs...

Anyway you seem to have duplicate entries which can be deleted from /etc/apt/sources.list.d/ while these errors shouldn't affect the update of MAG's repo and installation of harmattan-power-menu...