SharmTouring on "[Plugin: WordPress SEO by Yoast] Why Meta Description Disappear!‏"

All Meta Description Disappear after i save and publish the pages, when i try to edit content or any something else inside any page i found my self should write new Meta Description and title again and set everything again ! it's so hard to me to do it for more than 150 page every time i want to edit! so, please help me to do something save the Meta Description like before it was working very well and still on pages easy but i don't know Why Meta Description Disappear?

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