The !SkinSubFolder! directory should go directly within your
project file folder (as in C:/myproject/!SkinSubFolder!). Put it
back there and see if RH is happy. Also, make sure that the skin
you are trying to use is a folder within !SkinSubFolder! and that
there are files within the skin folder.
The !SSL! folder is the default place that your generated
output folders go. RH doesn't know to look there for the
skins.