Oracle Error ORA-12809: cannot set string_INSTANCES when mounted in exclusive mode

Oracle Error Message

ORA-12809: cannot set string_INSTANCES when mounted in exclusive mode

Reason for the Error

An attempt was made to set SCAN_INSTANCES or CACHE_INSTANCES using the ALTER SYSTEM command while the database was mounted in exclusive mode.

Solution

SCAN_INSTANCES / CACHE_INSTANCES may not be set unless running Oracle Real Application Clusters mounted in CLUSTER_DATABASE mode.