Any edit to .htaccess breaks Magento Site

Hi All,
This is my current .htaccess file:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

###########################################
## Deny access to cron.php
[…]

See original post by invalid@example.com (Borduhh)