This is not documented anywhere or I was not able to find it. When creating new skin it is mandatory to create
/css/altskin.css
even if the file is empty. XC is coded so if this file does not exists $AltSkinDir and $AltImagesDir variables have no value and are not assigned to smarty.
What altskin.css has to do with these 2 variable is beyond me
. Easily can call this a bug. It can be fixed by modifying smarty.php and taking out the conditional line
if (@file_exists($alt_skin_dir . XC_DS . 'css' . XC_DS . 'altskin.css')) {
or if you want to be forced to create an emtpy file for no reason at all just create altskin.css in your new skin css directory - which means you have to have css directory as well even if you don't need it....