Fabian on "[Plugin: WP-Filebase Download Manager] Update v 0.3.0.04 - "WP-Filebase not active" when editing posts"

In editor_plugin.php replace

// check if WP-Filebase is active
if(!in_array(basename(untrailingslashit(dirname(__FILE__))).'/wp-filebase.php',get_option('active_plugins')))
	wp_die('WP-Filebase not active.<!-- FATAL ERROR: WP-Filebase DISABLED -->');

with

include_once( ABSPATH . 'wp-admin/includes/plugin.php' );
// check if WP-Filebase is active
$wpfb_rpath = basename(untrailingslashit(dirname(__FILE__))).'/wp-filebase.php';
if(!is_plugin_active($wpfb_rpath))
	wp_die("WP-Filebase not active. ($wpfb_rpath not in [".implode(',',get_option('active_plugins'))."]) <!-- FATAL ERROR: WP-Filebase DISABLED -->");

This should at least give some debug output.

Are you running a multisite WordPress?