Multiple subgroup indexes are being used within the subgroup.
Explanation:
The articles within an article group can be divided into subgroups. The order of the subgroups within the article group can be indicated using the index of each subgroup. This index must have a unique value within the article group in order to determine the correct order. In this error message, several indexes have been assigned within one subgroup of one article group. A subgroup can of course only have one index.
Solution:
Ensure that the subgroups within the same article group have unique indexes assigned and only one index per subgroup.
