Installation Warning: mod_rewrite problem

I successfully installed Omeka!

But, now this:

Installation Warning

The following issues will not affect installation, but they may negatively affect the behavior of Omeka:

Unable to check for mod_rewrite

Unable to verify that mod_rewrite is enabled on your server. mod_rewrite is an Apache extension that is required for Omeka to work properly. Omeka is unable to check because your php.ini allow_url_fopen setting has been disabled. You can manually verify that Omeka mod_rewrite by checking to see that the following URL works in your browser:

What to do? TIA!!!