Plugin not listed

A simple Plugin did’nt work on Version 3.2.1 and 3.3.

Step 1:
Create the Plugin directory with the name “plugin-references” on wp-content/plugins/

Step 2:
Create the Main-File of the Plugin with the name “plugin-references.php” on wp-content/plugins/plugin-references/

Step 3:
Fill the Plugin-File with content:

<?php
	/*
		Plugin Name: Plugin Reference
		Plugin URI: http://hovida-design.de/
		Version: 1.0
		Author: Adrian Preuß
		Author URI: mailto:a.preuss@hovida-design.de
	*/

	function plugin_reference($content) {
		$content = str_replace("[plugin-reference]", "Hello, iam the Plugin!", $content);
		return $content;
	}

	add_filter('the_content', 'plugin_reference');
?>

Step 4:
Activate Plugin,..

The Plugin can’t be activated. The Plugin are not on the Plugin-List in the Administration.

On Frontend (if WP-Debug on) give PHP a error/warning:
Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /****/wp-includes/plugin.php on line 170