I have the exact same problem and the account given is the correct account code and still it says invalid account code. I have two accounts with IB. But I was still able to trade.
All those errors are generated by Traders Workstation, NOT AmiBroker.
You should complain to IB and they should explain why you get those errors.
AmiBroker does NOTHING, it just passes what you specify to TWS and displays TWS-generated errors back to you. If TWS produces error code it is TWS thing, not AmiBroker.
Interactive Brokers is the proper address of your questions.
IBController is open source, see: AmiBroker / IBController · GitLabThere is no PROCESSING inside. It is just passing things back and fourth.