I'm not a party to this situation, but I've been reading this thread and I'm surprised so many people don't know it's perfectly OK at IB to add alternate traders to one's account -- even an individual one. I did so myself for a period of several months, although both of us are in the U.S. Adding a 2nd trader is just another menu item on the IB site. Nothing there says it can't be overseas.
Other responders keep raising objections based on this being a foreign account, when he clearly said it's not. It's a U.S. account.
IB has customers all over the world. Unless they prohibit customers in country "X", they have no business being so sticky about a 2nd trader in that very country. Not, at least, unless they WARN YOU IN ADVANCE that this could be a problem unless you follow procedures a, b, and c and make sure not to violate rules x, y, or z, all of which they need to lay out for you.
Blindsiding a loyal longtime customer who only wants some trading help with this kind of "death penalty" doesn't seem logical. Especially without allowing him to cure the problem. They could simply disallow any secondary traders on his account, taking him back to status quo ante, to which of course they never had any objection.
I can think of only one possible reason for IB's action: If the customer created the 2nd trader under one identity, but actually the person doing the trading was someone else. After reading some of the comments on this thread I can see where they might object to that if the 2nd trader were overseas. But such an objection wouldn't have occurred to me before today.
Just a thought, but possibly the customer involved might be able to resume trading at IB if he was able to form a corporation, LLC, etc. where he was only a minority owner.