If your purchase agreement was subject to a mortgage commitment, then you can be released right away. You will need to provide a written letter to the seller or the seller's agent stating that you are cancelling the contract and the reasons why (refusal to sign a driveway easement letter). You could give the seller 24 or 48 hours to resolve the issue if you really want the house. If not then have the date of the letter be the cancellation date. You have a very good case here to be able to get back your earnest money deposit.