Query not working in sidebar widget

I created a Query to list thumbnails of posts from a category for a sidebar widget. I took a script I used to query posts on a home page which actually works very well but the one in the sidebar doesn’t work and I can’t figure out why.

Thanks for any tips how to fix it.

Code:

<?php
/* Plugin Name: Pohřešované osoby
Version: 1.0
Author: ....
*/
class ptPohrOsoby extends WP_Widget
{
  function ptPohrOsoby()
  {
    $widget_ops = array('classname' => 'ptPohrOsoby', 'description' => 'Obrázkový seznam pohřešovaných osob' );
    $this->WP_Widget('ptPohrOsoby', 'Pohřešované osoby', $widget_ops);
  }

  function form()
  {
?>
  Not editable atm.
<?php
  }

  function widget()
  {
    echo $before_widget; ?>

    <div class="title"> <p> Pátrání po osobách </p> <hr/> </div>

    <div class="patrani"> 

    <?php query_posts('cat=17&posts_per_page=4'); ?>
	<?phpif ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

		<div class="osoba">
			<div class="kraj <?php post_class(); ?>"> <?php global $post;
		   foreach(get_the_tags($post->ID) as $tag) {
		      echo $tag->name;
		 } ?> </div>
			<?php the_post_thumbnail( 'patrana_osoba' ); ?>
		</div>

	<?php endwhile; endif; ?>
	<?php wp_reset_query(); ?>

		<div class="clearer"></div>

		<hr/>

	</div>
<?php

    echo $after_widget;
  }

}
add_action( 'widgets_init', create_function('', 'return register_widget("ptPohrOsoby");') );
?>