Although the system can detect individual invalid intervals, it's still possible to create an invalid FIX schedulers with valid intervals that can't not be detected automatically by system.
The scheduler demonstrated below has the same exception interval as the schedule interval. A scheduler like this will never be triggered because the exception interval always "cancels" the schedule interval.
The scheduler demonstrated below has two "complementary" intervals. The combine scheduler will run continuously all the time. It will never stop.
The problems in schedulers shown above can not currently be detected programetically, although those schedulers don't make any sense in reality.
A problemtic scheduler may cause program errors or undetermined behaviour. Caution should be taken when designing schedulers to avoid problems!