Can not logout when activating plugin

When ULTIMATE FACEBOOK is activated, i cannot logout of my account. I get the following errors:

Warning: Cannot modify header information - headers already sent by (output started at /wp-includes/class.wp-scripts.php:125) in /wp-content/themes/Wp-Forest-2.4.4/users/login.php on line 13

Warning: Cannot modify header information - headers already sent by (output started at /wp-includes/class.wp-scripts.php:125) in /wp-includes/pluggable.php on line 697

Warning: Cannot modify header information - headers already sent by (output started at /wp-includes/class.wp-scripts.php:125) in /wp-includes/pluggable.php on line 698

Warning: Cannot modify header information - headers already sent by (output started at /wp-includes/class.wp-scripts.php:125) in /wp-includes/pluggable.php on line 699

... and so on until "line 881"