Denormalized group cannot be created since XML Element/Attribute <column name> has a many to many relationship with XML Element/Attribute <column name>.
You have at least two multiple-occurring element in the group with a many-to-many relationship.
You cannot put more than one multiple-occurring element with a many-to-many relationship in the same group. The multiple-occurring elements in a denormalized group must have a one-to-many relationship.