Whoops! The default skin for your wiki, defined in $wgDefaultSkin as $1, is not available.
Your installation seems to include the following skins. See Manual: Skin configuration for information how to enable them and choose the default.
$2
- If you have just installed MediaWiki
 -  You probably installed from git, or directly from the source code using some other method. This is expected. Try installing some skins from mediawiki.org's skin directory, by:
-  Downloading the tarball installer, which comes with several skins and extensions. You can copy and paste the 
skins/directory from it. -  Cloning one of the 
mediawiki/skins/*repositories via git into theskins/directory of your MediaWiki installation. 
 -  Downloading the tarball installer, which comes with several skins and extensions. You can copy and paste the 
 - Doing this should not interfere with your git repository if you're a MediaWiki developer.
 
- If you have just upgraded MediaWiki
 -  MediaWiki 1.24 and newer no longer automatically enables installed skins (see Manual: Skin autodiscovery). You can paste the following lines into 
LocalSettings.phpto enable all currently installed skins: 
$3
-  If you have just modified 
LocalSettings.php - Double-check the skin names for typos.