It has been solved, I'm glad about it and all... anyway the Breagar ACVIRGI issue should be related to the changes in the latest release of Questpack (ACVIRGI dialogue removed from the mod).
The previous release of Questpack added both Virginie creature and ACVIRGI dialogue. The current seems to add only Virginie creature... thus breaking Breagar ACVIRGI2 append.
The reason is that when Breagar finds Virginie creatures it tries to append the ACVIRGI2 dialogue to the non-existant ACVIRGI dialogue (previously added by Questpack).