Select "Use Asset Catalog" (I decided to just do this for application icons, not launch images, because my errors were not related to application icons, as it seems to you), and then drag the corresponding icons to their correct places.
The first time I did this, it was a little messed up, I believe, because I installed the resources, so in the end I selected "Do not use asset directories", which reset so that the resources are empty, deleted the asset directory and then again Select Use Asset Catalog.
At this point, all the spots were empty, and I was able to drag the right assets to the right places. Please note that there is no slot with the iOS 7x60pt icon.
I found this other related thread that had the answer: How do you update application icons and launch images to support iOS 6 and 7 at the same time?
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