You tried to upgrade your iPhone to iOS 4 via a virtual Windows machine running on VirtualBox, you then saw an error message said upgrading failed! What to do now???

Don’t panic! Take a look at the “USB” device icon on the bottom right corner, has your iPhone connected to the virtual machine? Yea, that’s the problem! You have to connect your iPhone several times during the while process. Just pay attention to that tiny icon, that’s it!