I haven't had any issues with the steam stuff ... Used the stand alone version from start .... Then added steam a short while back maybe 2 weeks and got back to stand alone client (I don't like steam lol dunno why).
He should try to change the server with an other client (just to make it easier for the support and maybe it works who knows?).
Hope they'll answer on his ticket and are able to fix his issue. Cause it's really annoying if you absolutely get no response at all (btw still no response on our ticket).
We "fixed" our issue temporarily .... thanks to Virtual Machines she's now running Windows and ... It works XD she's able to log into her account from the Virtual Windows but still can't login with her normal Mac OS.
I really got no clue what's the issue with this stuff cause it absolutely makes no sense to me but well.... Problem TEMPORARILY fixed but still hope to get a real solution.