aeiouHolidays are undefined but used by Slogan Rules
If you think this message is appearing erroneously, make sure that it is not caused by one or more of the a-e-i-o-u sets being selected in the Holidays Override property of one of the DiaryGridLines.
Cause : In the Slogan Rules of one of the DiaryGridLines, you have specified that one of the slogans should be skipped whenever a holiday occured for one of the aeiouHolidays Lists. However no Holidays Sets are associated with that Holidays List.
Consequences : The slogan will never be skipped, since there will never be an occurrence of a holiday in that Holidays List.
•Change List of Holidays Sets : Opens the corresponding Holidays List property editor, so you can select one or more Holidays Sets to use.
•Edit Holidays Rules : Let you add/modify holidays rules.
•Use one of the prefered Holidays Sets : At the bottom of this popup menu, you will find the "favourite" Holidays Sets as you have selected them in International Preferences. Note that you can only select one Holidays Set using this solution.
If the reference to a Holidays Set specified in the Slogans Rules options is erroneous (ie. you did not mean to have them set), you can just edit the corresponding Slogans property.