Andy Stoyle on "[Plugin: WordPress SEO by Yoast] Wordpress SEO affecting my permalinks"

It appears my Wordpress SEO Plugin is affecting my archive links on my blog page. They are pointing to my Home Page and not the monthly archive. When I deactivate the plugin it works fine. Any ideas?
Here's the link to the blog page which is a Pixeto Expressions theme.
http://www.alsphotography.co.uk/blog/
many thanks
Andy

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