page post error message

I get this error just below where I am writing a page while writing. The page saves ok anyway. what is this and why is it appearing?

WordPress database error: [Table ‘planetsc_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