Forbid the site's browsing to anyone but not to me

[eluser]TheFuzzy0ne[/eluser]
Try this:

Code:

RewriteEngine on
RewriteCond %{REQUEST_URI} !^/maintenance.php
RewriteCond %{REMOTE_HOST} !^127\.0\.0\.1
RewriteRule $ /maintenance.php [NC,L]

# If the URL starts with the following, redirect to the index.php.
# This is not necessary if you don't have your application or system directories in your Web root.
RewriteCond %{REQUEST_URI} ^/(system|application)
RewriteRule ^(.*)$ /index.php/$1 [L]

# Check to see if the file or directory exists. If it doesn't, re-route via index.php.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php/$1 [L]

The order was incorrect, so it was mangling the URL. I've also edited your existing .htaccess data to make it a little more robust.

If that doesn't work, you may need to substitute the IP address with your actual internal IP address. i.e 192.168.0.1, or whatever.