If you click on the icon menu work but if you click on the link below the icon, you will receive a page with app not found
So go on the includes/libs/ and open the admin.module.php

find the line

'<br />'.url('admin_menu',t('Menu')).'</div>

change to

'<br />'.url('admin/menu',t('Menu')).'</div>

Fiore

We will fix the link soon, thank you for you reporting.