Within the article group, one or more subgroups contain identical subgroup indexes.
Explanation:
Articles within an article group can be divided into subgroups. The index of each subgroup can be used to indicate the order of the subgroups within the article group. This index must have a unique value within the article group in order to be able to determine the correct order. In this error message, the same index is assigned to two or more subgroups of one article group.
Solution:
Make sure that the subgroups within the same article group have been assigned unique indexes.
