problem with e newsletter

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

i try with a simple texta as content in a wp 3.2..1 with no plugins activate