Given it sounds like several people who likely have more training than the advocate have clearly told you it isn't Asperger's, it sounds like maybe if the advocate can't move on it is time to find a new one who can keep her own experience separate and focus more on the specific needs your son has.
I certainly agree misdiagnosis is a huge problem. It is worth keeping in mind though that there certainly are gifted kids who have Asperger's so if parents are hearing over and over again that the child has AS it is worth investigating that with someone who understands giftedness.
