Once you and the seller have negotiated an offer and you've been pre-approved for a mortgage, you might think that you are in the clear as far as your closing goes. However, that is not always the case. Many surprising things can put a halt to closing. Some may ultimately stop the closing altogether while others could simply cause a delay. Here are a few unexpected things that can derail a real estate closing: A Job Promotion  While you might know that changing employers is one way to interfere with the closing, another deal-breaker can be switching positions with your current employer.…