Ok, so you are suggesting that the Wordfence plugin is not working on the Pianetadonna platform due to an incompatibility with another plugin.
As we use our Giallozafferano blog as a test site for our Pianetadonna blog we try to keep the installations and settings on both blogs in sync. As far as the plugins go, the same plugins are installed on both blogs. So I do not think it likely that the blocking of the Wordfence plugin is caused by an incompatibility with another plugin.
Do you have any other suggestions as to why the Wordfence plugin registration is blocked on the Pianetadonna platform and not on the Giallozafferano platform?