error/moodle/setting invalid ui label
This error will occur when the course being backed up (or copied/imported) contains a section with invalid characters in its name.
Due to a bug in the current validation code, any names that consist of whitespace characters are considered invalid and thus trigger this error.
Users that rely on "blank" section names (e.g. to prevent the display of Moodle's default category labels) are advised to
- remove the whitespace for the duration of the backup or
- replace it with a
HTML entity (which will add an empty line, unfortunately).