Error Message When I try to Save

I just upgraded to WordPress 2.3.1 from an older version. I’ve been working on a blog post, and I get this error message when I try to save it:

“WordPress database error: [Table ‘lifecraf_wrdp1.wp_post2cat’ doesn’t exist]
SELECT cat_ID AS ID, MAX(post_modified) AS last_mod FROM wp_posts p LEFT JOIN wp_post2cat pc ON p.ID = pc.post_id LEFT JOIN wp_categories c ON pc.category_id = c.cat_ID WHERE post_status = ‘publish’ GROUP BY cat_ID

Warning: Cannot modify header information – headers already sent by (output started at /home/lifecraf/public_html/wp-includes/wp-db.php:160) in /home/lifecraf/public_html/wp-includes/pluggable.php on line 391″

Anyone know what’s wrong?