title: VirtualBox upgrade trashed my virtual machine
body: <p>I had Virtual Box 3.2 working fine, emulating 32-bit Windows XP in a 64-bit Windows 7 host. Then I upgraded to VirtualBox 4.0.4, and everything seemed to work (after I installed a couple of things -- USB2.0 support, Guest Additions).<br>
  Then I restored a snapshot that was taken under version 3.2, and now I've lost everything. I get the error message:</p>
  
  <pre><code>The selected virtual machine is *inaccessible*. Please inspect the error message shown
  below and press the **Refresh** button if you want to repeat the accessibility check:
  
  Could not find an open hard disk with UUID {b0e666ef-1041-415a-8329-876b337e1958}.
  Result Code: 
  VBOX_E_OBJECT_NOT_FOUND (0x80BB0001)
  Component: 
  VirtualBox
  Interface: 
  IVirtualBox {d2de270c-1d4b-4c9e-843f-bbb9b47269ff}
  </code></pre>
  
  <p>I tried creating a new virtual machine from the vdi file, but it locks up when loading <code>WINDOWS\System32\DRIVERS\lfsfilt.sys</code>. I tried re-installing version 3.2, but I get exactly the same problems.  </p>
  
  <p>I have a <code>VirtualBox.xml</code> file in my <code>.VirtualBox</code> directory, and various files (Virtual Dell.xml, Virtual Dell.xml-prev etc.) in <code>.VirtualBox\Machines\Virtual Dell</code>.  </p>
  
  <p>Help please! How do I get my virtual machine back?</p>