I know it sounds dumb but I remember reading about someone who had a YubiKey but forgot to activate it in his MtGox security center.
Can you clarify? I see my Yubikey specifically under "Withdrawals".
You should be good then.
Haha, well apparently not since someone still managed to steal from my account. I added screenshots of the Yubikey. Yubikeys aren't supposed to be easy to crack are they? I can only think of Mt. Gox itself doing this so I will never trust them again.
I don't have any clue what went wrong in your case but at least you didn't forget to activate your YubiKey like I've already seen in the past.
Does the OTP value I see is Google Authenticator? If you did a backup of the seed somewhere it could have been stolen.