I fixed it by doing this:
- renamed the 'skins' folder to 'skins.old'
- creating a new folder named 'skins'
- logging into the game, entered a hangar, and checked the 'automatically download skins' button
- after several minutes, the file named 'skins.res' was downloaded to the new 'skins' folder
- verified that this file was missing from the original 'skins.old' folder
- copied the new skins.res file to the 'skins.old' folder
- deleted the newly created 'skins' folder
- renamed the 'skins.old' folder to 'skins'
- re-launched the game, and the skins were available
So, for some reason, the file 'skins.res' was deleted when I ran the update tonight.
(I tried to make this as basic a walkthrough as possible for everybody to understand) -- sorry if it comes across infantile.