Holiday Set used for associated holidays of aeiou-Namedays has been deleted
Source : DiaryGridline.
Cause : The Holidays Set associated (see Use Holidays Set below with Saints/Namedays) with one of the Namedays Sets of the Saints/Namedays Options of a DiaryGridline refers to a Holidays Set which no longer exists in the Holidays Sets database. Note that this message cannot be due to renaming, or moving a holidays set; this message is only triggered if the holidays set has been deleted.
•Change Holidays Sets : Opens the Saints/Namedays Options property editor, so you can remove references to this Holidays Set.