For those that don't know, a credit card issuer has every right to suddenly reduce your credit limit below the current balance of the card at any time without much notice. It is then perfectly OK for them to assess an over-limit fee because you are over your new credit limit. Tricky.
Lesson: Try to stay away from the upper reaches of your credit limit--don't ever use more than 90% on any one card.
http://consumerist.com/5170484/your-credit-card-limit-can-be-reduced-below-your-current-balance