Problem when posting to blog

I am not sure what I have done , but updated wordpress to the latest one but also may have deleted some files using Dreamweaver (not sure really??)

When I press publish to add a new post I get this message below.

WordPress database error: [Table ‘b13choc_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/b13choc/public_html/blog/wp-includes/wp-db.php:160) in /home/b13choc/public_html/blog/wp-includes/pluggable.php on line 391

If I then press the back button and view site the new posting appears ok.

So basicly, I can still post but get interrupted by this message every time.
If I need to replace a file, what is it and where do I put it.

As you can tell by the above, I am not too technical when it comes to WordPress, I can add plugin’s and change the look of the site and add content using ftp but that’s about it.

Any help much appreciated. Cheers in advance.
Kev