fatal error

I got the following error message while attempting to install a plug in (wpmailing). I crashed my site so when I log in there is nothing but what you see below:

Warning: Invalid argument supplied for foreach() in /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php on line 254

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-login.php on line 337

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-login.php on line 349

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-includes/pluggable.php on line 690

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-includes/pluggable.php on line 691

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-includes/pluggable.php on line 692

Warning: Cannot modify header information – headers already sent by (output started at /home/divajulz/public_html/wp-content/plugins/wpmailing/mailing.php:254) in /home/divajulz/public_html/wp-includes/pluggable.php on line 890

Please help. I don’t know how to fix this and I have lost everything!
Sincerely
Julie J.