Saving a note errors out saying that Notify Assignee or Notify Originator are required and can't be null
The automatic reminder that comes after the note has two values that are copied from the note. Notify Assignee and Notify Originator. If the user doesn't check one of the boxes on the note then it doesn't save any value, true or false. It writes a NULL to the database. And this is then copied to the reminder. The reminder requires a value, true or false so it errors out.
This is valid for 7.2.6 and newer.
In object designer modify the note object. Modify the Notify Assignee and Notify Originator attributes. Set their default value to false. This way if the user doesn't check them on the note value then the false will be copied to the reminder.