At first I wanna thanks Joost De Valk for developing such a good SEO plugin and host that plugin as free.
My problem is somewhat complicated. Here it is?
Yoast XML Sitemap was working fine in my single-user WordPress Installations but when I move my WordPress site multi-site. I saw that the Google webmasters tools was returning page-sitemap.xml as 404 not found and when I visit my sitemap I saw that everything was working fine. Then why did Google Webmasters returning my page-sitemap.xml as 404. Remember that I'm using WordPress multi-site.
I also read the most recent following thread on WordPress forums which is the same problem that I'm getting but that doesn't work for me.
What should I do? Any solution. Thanks in advance.