Just chiming in that this "Invalid bitcoin address, please confirm your input" BS is still alive and well. Count me as another screwed pooch. I can't even believe how cross this makes me... Mt. Gox can't expect to survive with this kind of "Paypal'esque" customer abuse can they?
Srsly wtf. Telling me my addresses are bad to cover their lack of funds? What evil. Do they care how much time I wasted trying addresses from 4 different wallets before coming here to find kindred souls?
Just happened to me too... but I clicked submit/confirm or whatever again and it worked the 4th time.
Oh well, happy to be out of gox anyway.

Yeah, got my btc out the next day after a customer support guy answered and said its a bug and that i should keep trying.... So i sat there like a pigeon at a laboratory cage feed reward button and kept bashing the pay button 4 or 5 times every 5 minutes. For an hour. It eventually worked. Bit i definitely ran up the internal index counter on my yubikey. Heh, not that it matters.
Fix this Mt Gox! It strikes fear in the hearts of your customers when you lock their funds!!!! Bug or not, there is little excuse.