At a glance

You need at least 2 regular (default) periods in the bell schedule.

What causes this error

Periods can be of different types (default, break, etc.). The generator requires at least 2 periods of the default type — the regular lesson slots — to build any timetable.

How to fix it

Go to Periods configuration and ensure at least 2 periods are marked as the default (lesson) type.

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