I'm getting the same thing using WP 2.3.1 and the latest sitemap 3.0.1 - Yahoo doesn't work. Additionally, here are just SOME of the errors shown in debug mode (it would be many pages if I posted them ALL :(
Notice: Undefined property: post_content in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_content_filtered in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_title in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_excerpt in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: comment_status in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: ping_status in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_password in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: to_ping in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: pinged in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: menu_order in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_mime_type in /home/roadside/public_html/blog/wp-includes/post.php on line 440
Notice: Undefined property: post_category in /home/roadside/public_html/blog/wp-includes/post.php on line 440