Oracle Error ORA-29381: plan/consumer_group string referred to by another plan and cannot be deleted

Oracle Error Message

ORA-29381: plan/consumer_group string referred to by another plan and cannot be deleted

Reason for the Error

An attempt was made to delete a plan or consumer group that is referred to by another plan.

Solution

Remove all plan directives that have the plan or consumer group as GROUP_OR_SUBPLAN; then delete the plan or consumer group.