Upgrade to 2.3.1 – WordPress database error

I’ve just upgraded WordPress to 2.3.1. I did a full backup of my database first, and followed the 3 steps install and it all seemed to go well, until I run the upgrade. I now have the following error message at the top of each page:

WordPress database error: [Table 'milk_wp1.wp_post2cat' doesn't exist]
SELECT ID, post_title, post_date, post_category FROM wp_posts, wp_post2cat WHERE post_author = 2 AND wp_posts.ID = wp_post2cat.post_id AND ID != 353 AND post_status = 'publish' AND post_date < NOW() GROUP BY ID ORDER BY post_date DESC LIMIT 5

Sometimes the message appears twice. Help please! What is going on, and how can I fix it?

Thanks