WordPress multisite

Create a Network of WordPress Sites
You cannot install a network of sites with your server address.
You cannot use port numbers such as :.
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Above is the error message I get after I have configured the wp.config.php file with the multisite line :-
define(‘WP_ALLOW_MULTISITE’, true);

I set up a subdomain with my hosting…what port numbers are they on about as none was shown on the error code above. I hopefully need a simple solution as I am not remote server savvy.