Short description:
If you add Settlers while your maximum population is already reached it gives a notification that tells you to upgrade your Store House.
Since the population maximum doesn't depend on Store House capacity, this is quite confusing.
Screenshot:
Possible cause:
Not relevant
Prevention:
Not relevant
Workaround:
Not relevant, but if you want to increase your population maximum you'll need to build or upgrade residences (Like Residence, Noble Residence etc)
Related:
Original thread(s): 1