Not sure of what you are trying to do with the nesting, but, does the nested Generic Annotation have the "Shared" box checked under Settings/Family Category and Parameters/Shared? IF so I have no answer, if not, edit the nested family, check, reinsert it, and see if you can tag to select the nested annotation to edit it. Not sure if Annotation families, especially within a titleblock will act the same as other family types. The combination of an annotation family, and a Title Block Family, may negate this ability.