Bundle not found

[Massimiliano Collavo]

"Fatal error: Class 'SimpleThings\ZetaWebmail\SimpleThingsZetaWebmailBundle' not found in /var/www/Symfony2/app/AppKernel.php on line 22"

AppKernel.php on line 22:
new SimpleThings\ZetaWebmail\SimpleThingsZetaWebmailBundle(),

The bundle is installed in
vendor/bundles/SimpleThings/ZetaWebmail

What's wrong??

thanks
Max