To me it looks like they run out of fiat. Took out a good few USD over the last few months of 2013, no problem. A couple of days ago a substantially smaller withdrawal got stuck, due to insufficient KYC. Rubbish, I'd say. Some of the questions they asked (ie address of SEPA bank) are already answered by their db. Others make hardly any sense. Not unlike MtGox last summer. The delays got longer and longer, the excuses weaker and weaker. bitstamp came up with KYC, mtgox told people they could only transfer whatever tiny amount per day due to bank restrictions.
When the fiat came surging in, they were able to pay out, now, with people trying to cash out and presumably no fresh money coming in, they struggle... Only thing, they should have got the money at some stage.