I was using the WordPress Automatic Upgrade Plugin to update an older wordpress site (which was still at that time, 2.2.1) and thought everything was fine until I made a new post.
The following message appears everytime a new post was made:
WordPress database error: [Table ‘mydatabase.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
In fact, it happened everytime when you moderate your comments or deleting the spam from Akismet as well. The weird part is that the post will actually work and will be still visible on your blog, but this is obviously a very annoying message that you will be much better off fixing now.
I found out later that I was using older version of the plugin Google XML Sitemaps. If you have an older version that is incompatible with WP 2.3, you will get the above error message whenever you try to post or moderate your comments.
The solution is: upgarde that plugin!
Google XML Sitemaps is one of my top 10 recommended wordpress plugins.