i can't use AH from one IP, on my other IP i can use the AH with the same account as i can't use it on my first IP.
Its strange, like my IP is flaged or so...
Today it worked for me again.
But i guess their "technical" problems are not over yet. Yesterday it went up and off within few seconds.
Fact is you are not the only one having that problem.
@Sinenomen: I don't think your IP is flagged. I guess Blizz only enable AH for an IP Range or just random IP's.
They try to go completly online or it's just another development fail idk.