I have trouble with my wordpress theme, the functions.php file ouputs ome bad header error:

Warning: Cannot modify header information - headers already sent by (output began at /home/slavisap/public_html/femarkets/wordpress/wordpress-content/styles/Flex E/functions.php:67) in /home/slavisap/public_html/femarkets/wordpress/wordpress-includes/pluggable.php online 934

It takes place at random, after i attempt to visit some page or create a different one from admin.

this really is my functions.php:

<?php
if (function_exists('register_nav_menus')) {
    register_nav_menus(
            array(
                'primary' => 'Primary Header Nav',
                'footer_menu' => 'Footer Menu',
                'exploring' => 'Exploring Page Menu',
                'using' => 'Using Page Menu',
                'downloading' => 'Downloading Page Menu'
            )
    );
}
function get_breadcrumbs() {
    global $wp_query;

    if (!is_home()) {

        // Start the UL
        echo '<ul class="breadcrumbs">';
        // Add the Home link
        echo '<li><a href="' . get_settings('home') . '">' . get_bloginfo('name') . '</a></li>';

        if (is_category()) {
            $catTitle = single_cat_title("", false);
            $cat = get_cat_ID($catTitle);
            echo "<li> &#47; " . get_category_parents($cat, TRUE, " &#47; ") . "</li>";
        } elseif (is_archive() && !is_category()) {
            echo "<li> &#47; Archives</li>";
        } elseif (is_search()) {

            echo "<li> &#47; Search Results</li>";
        } elseif (is_404()) {
            echo "<li> &#47; 404 Not Found</li>";
        } elseif (is_single()) {
            $category = get_the_category();
            $category_id = get_cat_ID($category[0]->cat_name);

            echo '<li> &#47; ' . get_category_parents($category_id, TRUE, " &#47; ");
            echo the_title('', '', FALSE) . "</li>";
        } elseif (is_page()) {
            $post = $wp_query->get_queried_object();

            if ($post->post_parent == 0) {

                echo "<li> &#47; " . the_title('', '', FALSE) . "</li>";
            } else {
                $title = the_title('', '', FALSE);
                $ancestors = array_reverse(get_post_ancestors($post->ID));
                array_push($ancestors, $post->ID);

                foreach ($ancestors as $ancestor) {
                    if ($ancestor != end($ancestors)) {
                        echo '<li> &raquo; <a href="' . get_permalink($ancestor) . '">' . strip_tags(apply_filters('single_post_title', get_the_title($ancestor))) . '</a></li>';
                    } else {
                        echo '<li> &raquo; ' . strip_tags(apply_filters('single_post_title', get_the_title($ancestor))) . '</li>';
                    }
                }
            }
        }

        // End the UL
        echo "</ul>";
    }
}
?>

this site URL: http://slavisaperisic.com/femarkets/wordpress/

are you aware what I am doing wrong?

Since there's no line 67 within the functions.php file you published (a minimum of, the version I copy/copied and pasted into my editor), I am speculating you've additional whitened-space at the start and/or finish of the functions.php file (prior to the opening <?php or following the closing ?> tags).

Any figures inside a PHP file outdoors the <?php ?> tags is treated as standard output and immediately written to STDOUT (or to the net servers output stream) as well as in an internet server scenario this makes headers to become sent, since what you're outputting may be the body from the response.

Make certain the opening < may be the first character within the file, and also the closing > may be the last character within the file.

You really don't have to incorporate a closing ?> tag if all of the data within the file is PHP code, and omitting it can help to prevent problems such as this...