Error setting up a Mutlisite

I’m getting this error when trying to install the setup:

Warning: is_writable() [function.is-writable]: open_basedir restriction in effect. File(/) is not within the allowed path(s): (/home/loumaph140/:/tmp:/var/tmp:/usr/local/lib/php/) in /home/loumaph140/domains/thyraxx.biz/public_html/wp-admin/includes/misc.php on line 170

.htaccess:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]