Extension talk:Stale Pages
There is a bug in the StalePages.php file for version 1.15 that causes the special pages page to fail.
Change:
$wgExtensionAliasesFiles['Stalepages'] = $dir . 'Stalepages.alias.php';
to
$wgExtensionAliasesFiles['Stalepages'] = $dir . 'StalePages.alias.php';
to resolve the problem