Oracle Message ORA-09979 - skxfqhsnd: Error Sending a message to another endpoint

ERRORskxfqhsnd: Error Sending a message to another endpoint
CAUSEThe process was unable to send a message to an existing endpoint.
ACTIONCheck that the other node(s) are part of the cluster and operating properly. Check the instance and processes on the other node(s). Correct the operating system error and retry the operation.