ORA-01567: dropping log string would leave less than 2 log files for instance string (thread string)

ORA-01567: dropping log string would leave less than 2 log files for instance string (thread string)

Cause: Dropping all the logs specified would leave fewer than the required two log files per enabled thread.

Action: Either drop fewer logs or disable the thread before deleting the logs. It may be possible to clear the log rather than drop it.