ady90 on "[Plugin: WordPress SEO by Yoast] Error submitting sitemap in google web master tool"

this is the error i am facing while submitting in google web master tool
"Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead."
help me to fix it

my website url is
http://www.shinedeals.com
and sitemap url is
http://shinedeals.com/sitemap_index.xml

http://img706.imageshack.us/img706/2084/wmterror.png
this is error screenshot

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