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please check it, I put the fix at:
/modules/mod_community_birthdays/helper.php line 45
from
$query = "SELECT user_id, DATE_FORMAT(value,'%d-%m') as php_date,DATE_FORMAT(value,'%W, %M %e') as formatted_date, TIMESTAMPDIFF(YEAR,value,CURDATE()) AS age, DATE_FORMAT(value,'%m%d') as value FROM ".$db->quoteName('#__community_fields_values')." WHERE "
.$db->quoteName('field_id')."=".$db->quote($fieldId);
to
$query = "SELECT user_id, DATE_FORMAT(value,'%W, %M %e') as php_date,DATE_FORMAT(value,'%W, %M %e') as formatted_date, TIMESTAMPDIFF(YEAR,value,CURDATE()) AS age, DATE_FORMAT(value,'%m%d') as value FROM ".$db->quoteName('#__community_fields_values')." WHERE "
.$db->quoteName('field_id')."=".$db->quote($fieldId);