Several Problems. CanI downgrade it?

Hey, I’ve got several problems since I upgraded to 2.3 (bad move, it’s was working nice).

1- When I save a post, I go to a screen like (sorry to post it)

WordPress database error: [Table ‘zagg.wp_post2cat’ doesn’t exist]
SELECT YEAR(post_date) AS year, MONTH(post_date) AS month, category_id FROM wp_posts INNER JOIN wp_post2cat ON (wp_posts.ID = wp_post2cat.post_id) WHERE post_date > 0 AND ID = 314 ORDER By post_date DESC

WordPress database error: [Table ‘zagg.wp_post2cat’ doesn’t exist]
SELECT DISTINCT YEAR(p.post_date) AS year FROM wp_posts p INNER JOIN wp_post2cat p2c ON (p.ID = p2c.post_id) WHERE p.post_date > 0 ORDER By p.post_date DESC

WordPress database error: [Table ‘zagg.wp_post2cat’ doesn’t exist]
SELECT DISTINCT MONTH(p.post_date) AS month FROM wp_posts p INNER JOIN wp_post2cat p2c ON (p.ID = p2c.post_id ) WHERE YEAR(p.post_date) = 2007 AND p.post_date_gmt < ‘2007-10-01 12:59:58’ ORDER By p.post_date DESC

WordPress database error: [Table ‘zagg.wp_post2cat’ doesn’t exist]
SELECT DISTINCT MONTH(p.post_date) AS month FROM wp_posts p INNER JOIN wp_post2cat p2c ON (p.ID = p2c.post_id ) WHERE YEAR(p.post_date) = 2006 AND p.post_date_gmt < ‘2007-10-01 12:59:58’ ORDER By p.post_date DESC

WordPress database error: [Table ‘zagg.wp_post2cat’ doesn’t exist]
SELECT DISTINCT MONTH(p.post_date) AS month FROM wp_posts p INNER JOIN wp_post2cat p2c ON (p.ID = p2c.post_id ) WHERE YEAR(p.post_date) = 2005 AND p.post_date_gmt < ‘2007-10-01 12:59:58’ ORDER By p.post_date DESC

Warning: Invalid argument supplied for foreach() in /web/sites/zagg.com.br/wp-content/plugins/af-extended-live-archive/af-extended-live-archive-include.php on line 294

Warning: Invalid argument supplied for foreach() in /web/sites/zagg.com.br/wp-content/plugins/af-extended-live-archive/af-extended-live-archive-include.php on line 294

Warning: Invalid argument supplied for foreach() in /web/sites/zagg.com.br/wp-content/plugins/af-extended-live-archive/af-extended-live-archive-include.php on line 294

WordPress database error: [Table ‘zagg.wp_categories’ doesn’t exist]
SELECT cat_ID, cat_name, category_nicename, category_parent FROM wp_categories c WHERE c.cat_ID > 0 ORDER BY c.cat_ID asc

WordPress database error: [Table ‘zagg.wp_categories’ doesn’t exist]
SELECT c.cat_ID, COUNT(distinct p2c.post_id) AS cat_count FROM wp_categories c INNER JOIN wp_post2cat p2c ON (c.cat_ID = p2c.category_id) INNER JOIN wp_posts p ON (p.ID = p2c.post_id) WHERE p.post_status = ‘publish’ AND p.post_date_gmt < ‘2007-10-01 12:59:58’ GROUP BY p2c.category_id

Warning: Invalid argument supplied for foreach() in /web/sites/zagg.com.br/wp-content/plugins/af-extended-live-archive/af-extended-live-archive-include.php on line 461

Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 83 bytes) in /web/sites/zagg.com.br/wp-includes/post.php on line 440

Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 81 bytes) in /web/sites/zagg.com.br/wp-includes/plugin.php on line 141

2- There’s a message on the left side bar like that

WordPress database error: [Unknown column ‘a’ in ‘order clause’]
SELECT * FROM wp_posts WHERE (post_type = ‘page’ AND post_status = ‘publish’) AND ( ID <> 0 ) ORDER BY a ASC

3- And the characters went strange. I write in portuguese so things like ç ã é and á got completelely changed.

How can I download my site?