Gabriela,
as I also learned last week, the latest Personas note (the one you mentioned) comes with the newest Personas client which introduces a new certificate, compared to the earlier clients. So essentially, if you install the latest client (which you should), then you have to repeat the steps explained in note 2025591 to register the new security certificate. Make sure to import and store the new certificate in both the 'Trusted publishers' and the 'Trusted root certification authorities' certificate store and the elevated trust mode will work again.