Here's their explanation:
"Looks like there is a technical issue and we have already escalated this to our developers and they are currently looking in to this and we are expecting to have this issue resolved soon and we will keep you updated once your withdrawal is processed form our end and we apologize for the inconvenience that this may have caused. "
And the cat ate my homework. Right.
A legit broker would follow that with "We have credited your account at ... bank with $$$ while we resolve our internal problems."
Somehow, all of Mt. Gox's "problems" result in them keeping your money.