Infinate SEO sitemap url seems to be invalid

I have the Infite SEO on a multi site with the multi-site option enabled for the plug-in.
When I go the the Settings>Infinate SEO for the site in question, I see the following 2 parameters:

Path to XML sitemap: /Library/Server/Web/Data/Sites/Wordpress/wp-content/uploads/sites/20/sitemap.xml

URL to XML sitemap:

There is an xml file on the server, but clicking the link give me an error in a browser: The requested URL /sitemap.xml was not found on this server.

I'm sure its a setting somewhere that needs to be modified, but I've not been able to find it after a long search. Please help!

Kind regards,

Allart van Holten