Drupal 7 Domain Access Module Gives 500 error, WSOD for subdomains
OK, might as well add a tentative answer on this one.

Add your subdomains using ServerAlias within the same single VirtualHost, because they all have the same document root.

ServerName www.example.com
ServerAlias drupalx.example.com
ServerAlias drupaly.example.com


Fix the stray rewrite stanza in virtualhost scope.

e.g put it inside the Directory block.

&lt;Directory "C:\xammp\www"&gt;
  &lt;IfModule mod_rewrite.c&gt;
    RewriteEngine on
    # Rewrite URLs of the form 'x' to the form 'index.php?q=x'.
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_URI} !=/favicon.ico
    RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]
  &lt;/IfModule&gt;
&lt;/Directory&gt;


However, the latter isn't really needed if using the default .htaccess file in your doc root. Alternatively, remove .htaccess and copy its contents to the Directory block instead.