Hey there!
Looks as if you have URL file-access disabled on your server, which will mean that it’s impossible for the importer to load the XML file to import from.
This should hopefully be an easy thing to sort out on your hosting, if you follow this guide: http://www.solo-technology.com/blog/2010/04/07/quick-fix-for-url-file-access-is-disabled-issues/
The easiest solution to try would be adding the following to your .htaccess file in the root of your website:
php_flag allow_url_fopen on
If this doesn’t work – then either have a look to see if you can change it on your server, or ask your host, they should be happy to enable it for you.
Hope that helps!
– Ed