[Plugin: Google Monthly XML Sitemap] error publishing posts

I have this when i try to publish posts or upgrade something:

Execution Stopped at this point: /home/yourweb/public_html/domain.com/wp-content/uploads/ap-sitemap/sitemap-ap-2011-02.xml
You Have probably some issue with your post_date that is set to 0000-00-00

http://wordpress.org/extend/plugins/google-monthly-xml-sitemap/