thurmansevolution blank schedules (schedules with no schedule items) were never intended to be supported. To avoid the "no schedule items" error, your schedules must all have at least one item.
As it says on the editor page, the alternate schedules are:
In priority order from top to bottom. The bottom entry will always match all days and all months, as a catch-all.
If you want a schedule to show an "offline" message of some sort on days where you don't have anything higher priority scheduled, create a schedule with your offline image (could even use an image library), or filler content, etc as the only schedule item set to flood. Move that schedule to the bottom of the prioritized list, and ETV will automatically mark it as matching all days.
If you don't intend to have full days that are offline, just accept that your lowest priority schedule will match all days, even if it's your "weekday" schedule. That's fine as long as the higher priority items match the days you don't want it to run on (e.g. weekends).
The two key points are:
- ETV will never let you create a prioritized list where a day will match no schedules; it does this by always making your lowest priority item match every day.
- ETV does not support empty schedules