If you use mod_security on your server you might encounter that a website script is not compatible with mod_security. To disable mod_security (v2) for a website, add the following code into the apache directives field:
<IfModule mod_security2.c>
SecRuleEngine Off
</IfModule>
For the older mod_security 1 version, use these configuration directives:
<IfModule mod_security.c>
SecFilterEngine Off
</IfModule>
Thanks to Planetfox for this tipp.