Cannot modify header information

When I edit or create a new sermon I get sent to an error page. It still updates and creates the sermon but there is obviously a problem.

This is the error:

Notice: Trying to get property of non-object in /home/lifepoi7/public_html/wp-content/plugins/sermon-manager-for-wordpress/includes/types-taxonomies.php on line 18

Warning: Cannot modify header information – headers already sent by (output started at /home/lifepoi7/public_html/wp-content/plugins/sermon-manager-for-wordpress/includes/types-taxonomies.php:18) in /home/lifepoi7/public_html/wp-includes/pluggable.php on line 1195

This is line 18 of the types-taxonomies.php:

$service_type = $term->slug;

This is lines 1192-1198 of pluggable.php:

if ( !$is_IIS && PHP_SAPI != ‘cgi-fcgi’ )
status_header($status); // This causes problems on IIS and some FastCGI setups

header(“Location: $location”, true, $status);

return true;
}
endif;