I added at the end

<IfModule mod_security.c>
SetEnvIfNoCase Content-Type \
"^multipart/form-data;" "MODSEC_NOPOSTBUFFERING=Do not buffer file uploads"
</IfModule>

<IfModule mod_gzip.c>
mod_gzip_on No
</IfModule>

I checked /incluedes/config.php and use real path

$config['basedir'] = "/home/CPANELNAME/public_html";
$config['baseurl'] = "http://www.MYSITE.com";

but still having this error.. What else can I check?
The host is hostonnet, and the other script I installed in another domain (2.4) works fine