Why does VirtualBox crash when I finish the install of BackTrack?

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http://unix.stackexchange.com – I have a windows 7 64-bit machine in which I have installed VirtualBox and decided to install BackTrack. The installation finished fine, but when it asked me to "please remove installation media and close the tray (if any) then press ENTER" VirtualBox crashes. I have tried going through the installation process twice but it has crashed both times. Additional Info just in case: Host operating system: windows 7 64-bit 6GB of RAM, I5 (HowTos)