Provided are a computer program product, system, and method embodiments for reverting from a new security association to a previous security association in response to an error during a rekey operation. The responder maintains a first security association with the initiator having a first key to use to encrypt and decrypt messages transmitted with the initiator. The responder receives a message from the initiator for a rekey operation to establish a second security association with the initiator using a second key. The responder queues Input/Output (I/O) for transmission using the second key after completing the rekey operation. After activating the second security association, the responder receives a revert message from the initiator to revert back to using the first security association and first key in response to a failure of the rekey operation.