I solved the same problem I had. It was to delete all the default folders:
"Click on the cog icon at the top right corner of the sky preset window, select "Append Defalt Skies...". All the default sky preset folders should be appended to the end of your presets list now. You can then delete all your old presets folders. Click on any of default sky preset that is just appended, and see if it works. Then you can add your own sky preset one at a time by clicking the "+" button."
This was a solution I found in the forums. But I deleted all the default skies first, then restarted PS and his the append menu item. The default skies came back. I had to re-load the skies I had added before, but now everything works as advertised.