Cannot delete or update a parent row:

运行时出现了这个错误，哪位好心帮我看看，急……
Caused by: com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`jbpm`.`jbpm4_execution`, CONSTRAINT `FK_EXEC_INSTANCE` FOREIGN KEY (`INSTANCE_`) REFERENCES `jbpm4_execution` (`DBID_`))
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:931)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1631)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1723)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3283)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1332)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1604)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1519)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1504)
at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:2551)