[Plugin: WordPress SEO by Yoast] I am getting a 404 error when I check for XML Sitemap

Any help would be appreciated. I am getting a 404 error when I click the button to get my xml sitemap???? Please help. Website is http://www.laserdiscworld.com. I am not getting ranked at all on google and this could be why. I was always ranked very high for all kepywords, now I cant even be found.

http://wordpress.org/extend/plugins/wordpress-seo/