Since you haven't provided an SSCCE it is rather hard to say with certainty but the suspicion has to be that your @AoA is incorrectly formed and may not even be an AoA at all. Perhaps it is a deeper structure but that's pure speculation since you have not shared it.

Update: GotToBTru looks to have found the likely reason. I can't imagine why Anonymonk changed that from my example.