Forums / Cotonti / Extensions / Support / Page siblings errors

Did you download similar pages for siena from here? Well, it might be really broken if SQL query crashed during installation of that plugin. If it was just partially installed, it explains the behavior you described. Then you can get rid of the errors by fixing it in phpMyAdmin manually:

DELETE FROM cot_plugins WHERE pl_code = 'similar';
DELETE FROM cot_config WHERE config_cat = 'similar';
DELETE FROM cot_auth WHERE auth_option = 'similar';
TRUNCATE TABLE cot_cache;