Help! Website stop working after search…where is problem?

Hello.

I set up plugin on one of my websites.

The problem occurs when a visitor starts search on my set up criteria. In that moment site crashes and this is what sql perform:

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id)
INNER JOIN wp_postmeta AS mt2 ON (wp_posts.ID = mt2.post_id)
INNER JOIN wp_postmeta AS mt3 ON (wp_posts.ID = mt3.post_id)
INNER JOIN wp_postmeta AS mt4 ON (wp_posts.ID = mt4.post_id)
INNER JOIN wp_postmeta AS mt5 ON (wp_posts.ID = mt5.post_id)
INNER JOIN wp_postmeta AS mt6 ON (wp_posts.ID = mt6.post_id) WHERE 1=1 AND wp_posts.post_type IN (‘post’, ‘page’, ‘attachment’) AND (wp_posts.post_status = ‘publish’ OR wp_posts.post_author = 1 AND wp_posts.post_status = ‘private’) AND ( (wp_postmeta.meta_key = ‘search_by_type’ AND CAST(wp_postmeta.meta_value AS CHAR) = ‘Free’)
OR (mt1.meta_key = ‘search_by_layout’ AND CAST(mt1.meta_value AS CHAR) != ‘get_all_cmf_except_me’)
OR (mt2.meta_key = ‘search_by_design’ AND CAST(mt2.meta_value AS CHAR) != ‘get_all_cmf_except_me’)
OR (mt3.meta_key = ‘search_by_columns’ AND CAST(mt3.meta_value AS CHAR) != ‘get_all_cmf_except_me’)
OR (mt4.meta_key = ‘search_by_sidebar’ AND CAST(mt4.meta_value AS CHAR) != ‘get_all_cmf_except_me’)
OR (mt5.meta_key = ‘search_by_thematics’ AND CAST(mt5.meta_value AS CHAR) != ‘get_all_cmf_except_me’)
OR (mt6.meta_key = ‘search_by_features’ AND CAST(mt6.meta_value AS CHAR) != ‘get_all_cmf_except_me’) ) GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 8

Where could be the problem? Why does website stop working at that moment?

http://wordpress.org/plugins/advance-wp-query-search-filter/