"If and when a client's vacation plans go wrong, it is never a pleasant experience for anyone. I am never happy when something happens that potentially upsets my client's vacation plans. Lucky for me, this rarely occurs and when it does, we have a great customer care team that helps resolve the matter promptly."

Be careful how you answer this question. Being negative about a job and an employer that you are trying to give all the best impressions is a tricky one as you don't want your answer to be personally set against you if you are hoping to be offered the position! Try and come up with an aspect beyond your control like the red tape and all the paperwork and jurisdiction you have to go through when obtaining visas and permission grants to volatile foreign places. That way it is not something personal (like not enough coffee breaks!) so the interviewer will not be able to think you might have a lazy attitude if they employed you.