Forwarding not working -> blank page

Greetings,

I am having a little error while trying to redirect on a page i have made. It doesn't want to redirect me at all, and just gives me a blank page, where it should be forwarding. The only thing i notice is when i select my URL (www.sitename.domain/plugin/filter) in the browser and hit enter it redirects me to the main page and i get a message saying "Form is missing __token or __ts fields".

My code looks like this:

The redirect action content in the actions folder "filter.php":

if (!isloggedin()) {forward();}
        // get the form input
          $filter = get_input('filterin');
          $text = get_input('body');
          $_SESSION['filter'] = $filter;
          $_SESSION['body'] = $text;
        // Forward
        forward('ad/filtered.php');

Action registered in "start.php" of the plugin:

register_action("pluginname/filter",false,$CONFIG->pluginspath . "pluginname/actions/filter.php");

And my form looks like following :

<h2><?php echo elgg_echo('adfilter'); ?></h2>
    <div class="adcategories">
        <form action="<?php echo $vars['url']; ?>action/<?php echo $action; ?>" enctype="multipart/form-data" method="post">
            <div>
            <?php echo elgg_view('input/securitytoken'); ?>
            </div>

            <div>
                <label><?php echo elgg_echo('adfilter_by'); ?></label><br />
                <?php echo elgg_view('input/pulldown',array('internalname' => 'filterin', 'options_values'=>array('tipo'=>elgg_echo('adtype'),'price'=>elgg_echo('adprice'),'isbn'=>elgg_echo('ad:isbn'))/*,'value'=>$vars['entity']->gender*/)); ?>
            </div>

            <div>
                <label><?php echo elgg_echo('adkeyword'); ?></label><br />
                <?php echo elgg_view('input/text',array('internalname' => 'body')); ?>
            </div>

            <div>
                <input type="submit" name="submit" value="<?php echo elgg_echo('filter'); ?>" />
            </div>
        </form>
    </div>

Appreciate any help and insights into this matter.