Cannot get custom skins to show up

I'm undoubtedly doing something really obvious, but I can't seem to get custom skins to work.

Normal installation using Kama or any of the supplied skins works fine.

I used v2 as the base, copied it and and renamed it v3. I've changed the references to "v2" in v3/skin.js to "v3", and I've tried config.skin = "v3" AND config.skin = "v3,/plugins/ckeditor/skins/", but the replacement doesn't show up.

In Firebug I can see an error r is undefined in ckeditor.js on line 20.

If anyone can spot what I'm doing wrong, I'd be very thankful for your advice.