LESS Compiler PHP with WordPress 4.0.1 and Bootstrap 3

I’m trying to add a php-compiler in my new WordPress Theme. Therefore I followed this Tutorial: http://www.tailored4wp.com/how-to-use-less-auto-compiler-in-your-next-wordpress-project-quick-tip-361/

My functions.php

/**
* LESS Compiler.
*/
function autoCompileLess() {

    // include lessc.inc
    require_once( get_template_directory().'/less/lessc.inc.php' );

    // input and output location
    $inputFile = get_template_directory().'/less/bootstrap.less';
    $outputFile = get_template_directory().'/css/bootstrap_less.css';

    // load the cache
    $cacheFile = $inputFile.".cache";

    if (file_exists($cacheFile)) {
        $cache = unserialize(file_get_contents($cacheFile));
    } else {
        $cache = $inputFile;
    }

    $less = new lessc;
    // create a new cache object, and compile
    $newCache = $less->cachedCompile($cache);

    // output a LESS file, and cache file only if it has been modified since last compile
    if (!is_array($cache) || $newCache["updated"] > $cache["updated"]) {
        file_put_contents($cacheFile, serialize($newCache));
        file_put_contents($outputFile, $newCache['compiled']);
    }
}
/**
 * Enqueue scripts and styles.
 */
function scripts() {

    wp_enqueue_style( 'bootstrap-css', get_template_directory_uri() . '/css/bootstrap_less.css' ); 
}
add_action( 'wp_enqueue_scripts', 'scripts' );

If I change some less files, there won’t be any file in output-directory. (I set the right permissions)

And if I add

if(is_user_logged_in()) {
add_action(‘init’, ‘autoCompileLess’);
}

…/wp-admin will show a blank page with no code in it. What’s wrong?

********EDIT*************

I copied the Theme to XAMPP Installation and got these Errors:

Fatal error: Uncaught exception ‘Exception’ with message ‘parse error:
failed at &:extend(.clearfix all);
D:xampphtdocswordpress/wp-content/themes/templateName/less/mixins/grid.less
on line 11′ in
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php:3460
Stack trace: #0
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php(2273):
lessc_parser->throwError() #1
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php(121):
lessc_parser->parse(‘// Grid system?…’) #2
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php(753):
lessc->tryImport(Array, Object(stdClass), Object(stdClass)) #3
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php(162):
lessc->compileProp(Array, Object(stdClass), Object(stdClass)) #4
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php(147):
lessc->compileImportedProps(Array, Object(stdClass), Object(stdClass),
Object(lessc_parser), ‘D:xampphtdocs…’) #5
D:xampphtdocswordpressw in
D:xampphtdocswordpresswp-contentthemestemplateNamelesslessc.inc.php
on line 3460