Cannot delete plan if it has variables

2011-03-21 16:12:18,574 ERROR [QuartzScheduler_Worker-3] [DeletionServiceImpl] Could not delete plan 'CONN-NOREPO'
org.springframework.dao.DataIntegrityViolationException: Hibernate operation: Could not execute JDBC batch update; SQL []; The DELETE statement conflicted with the REFERENCE constraint "FK38458EF6D5BADF1". The conflict occurred in database "bamboo", table "dbo.VARIABLE_DEFINITION", column 'PLAN_ID'.; nested exception is java.sql.BatchUpdateException: The DELETE statement conflicted with the REFERENCE constraint "FK38458EF6D5BADF1". The conflict occurred in database "bamboo", table "dbo.VARIABLE_DEFINITION", column 'PLAN_ID'.
Caused by: java.sql.BatchUpdateException: The DELETE statement conflicted with the REFERENCE constraint "FK38458EF6D5BADF1". The conflict occurred in database "bamboo", table "dbo.VARIABLE_DEFINITION", column 'PLAN_ID'.