Set the 'ServerName' directive Globally to suppress this message.

Hi

I have used this command to check if mod_rewrite was activated

/usr/local/apache/bin/httpd -M|grep rewrite

It is but I get a message asking to: Set the 'ServerName' directive Globally to suppress this message.

try checking file /etc/hosts if you have there your server name set.
If not you can edit that file or try to save your hostname again from CWP hostname change module.