Yes,AuthNet support requested the transaction and profile id as part of their investigation. They claim that American Express authorized the fake card number and everything on their end is working properly. However, I pointed out to them that AIM will reject that card number so that explanation does not really seem plausible. I haven't gotten any further responses from them.
I am not sure if it's only American Express as I tested with Amex first and didn't test any other card types once it had failed. At this point, I have my solution of using AIM to submit a 1 cent transaction and voiding it immediately afterwards to verify card numbers.
