[Plugin: WordPress SEO by Yoast] Google Crawler is showing 404 error for my blog pages…why so?

I have a blog, couponspicy.com, i am using Yoast SEO plugin for SEO Work.

Which is generating page address in such a manner.

Store Name: Canvas On Demand
Slug: canvas-on-demand-coupon-codes
Link format: http://www.couponspicy.com/stores/%5BSLUG NAME]
Proper link of the page: http://www.couponspicy.com/stores/canvas-on-demand-coupon-codes

The problem is Google Crawler is showing my slug name with 404 error, it says i dont find this page. where as if i type http://www.couponspicy.com/stores/canvas-on-demand-coupon-codes/ in address bar, it show up the page.

Any help would be highly appreciated.

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