i have a ploblem whit enewsletter plugin

when i send a newsletter
i have this error
Warning: mysql_real_escape_string() expects parameter 1 to be string, object given in /www/docs/mundoagro.cl/public_html/wp/wp-includes/wp-db.php on line 774

Warning: Cannot modify header information - headers already sent by (output started at /www/docs/mundoagro.cl/public_html/wp/wp-includes/wp-db.php:774) in /www/docs/mundoagro.cl/public_html/wp/wp-includes/pluggable.php on line 934