I recently had a similar problem under MSWindows 10, and it was solved when under the « contextual menu = Propriétés / tab = Sécurité » of the DLL file (My PC language is French, I am not sure what the labels are in English), I clicked on « Modifier » button to remove all the goups/users but myself. The issue was that the order of them was masking my privileges.

With the « Avancé » button, one gets a pannel in which the « Accès effectif » allows to check that the privileges are in effect what they are configured. That was not the case before I removed other users/groups.