Real Estate Agent or Real Estate Law answers please.?

I am a realtor and I have a very odd situation. I represent a buyer who put in an offer on a short sale home. After 6 months we finally got the approval letter from the bank giving the thumbs up on the purchase price, and also listing the requirements to close. My client paid for inspections on the house as well as getting the appraisal done and everything came back great. Title company submitted the final HUD two days before our scheduled closing and the bank investor came back and said they would not approve the final HUD for closing and they have decided they want their net proceeds to be more...$5500 more. The house itself was appraised at less than what they are now asking for, which Im not sure how they can get that price. My question is, is there any legal action I can take, or my client, against this bank for the stunt they are pulling? It has been a total of 9 months working on this deal, and everything was already approved 6 months in, by the bank, and now they are trying to change the price. My client has forked out money for this house, based on this original approval. I want to sue the F*%# out of this bank if possible.