title: Why could VirtualBox not find a registered machine named Windows_7?
body: <p>I'm trying to change TCP/UDP of a virtual machine using VBoxManage setextradata.</p>
  
  <p>Whenever I type the command:</p>
  
  <pre>sudo VBoxManage setextradata Windows_7 "VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestEmule_TCP/Protocol" TCP</pre>
  
  <p>I get the following error:</p>
  
  <pre>VirtualBox Command Line Management Interface Version 2.1.4
  (C) 2005-2009 Sun Microsystems, Inc.
  All rights reserved.
  
  [!] FAILED calling a->virtualBox->FindMachine(Bstr(a->argv[0]), machine.asOutParam()) at line 3688!
  [!] Primary RC  = VBOX_E_OBJECT_NOT_FOUND (0x80BB0001) - Object corresponding to the supplied arguments does not exist
  [!] Full error info present: true , basic error info present: true 
  [!] Result Code = VBOX_E_OBJECT_NOT_FOUND (0x80BB0001) - Object corresponding to the supplied arguments does not exist
  [!] Text        = Could not find a registered machine named 'Windows_7'
  [!] Component   = VirtualBox, Interface: IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}
  [!] Callee      = IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}</pre>
  
  <p>The virtual-machine has been created using GUI. Any idea?</p>
  
  <pre>$ cd /Users/marco/Library/VirtualBox/Machines/Windows_7
  $ ls
  Logs                Windows_7.xml
  Windows 7.xml.1.5-macosx.bak
  $ sudo vboxmanage registervm Windows_7.xml
  VirtualBox Command Line Management Interface Version 2.1.4
  (C) 2005-2009 Sun Microsystems, Inc.
  All rights reserved.
  
  [!] FAILED calling a->virtualBox->OpenMachine(Bstr(a->argv[0]), machine.asOutParam()) at line 762!
  [!] Primary RC  = NS_ERROR_FAILURE (0x80004005) - Operation failed
  [!] Full error info present: true , basic error info present: true 
  [!] Result Code = NS_ERROR_FAILURE (0x80004005) - Operation failed
  [!] Text        = Could not lock the settings file '/var/root/Library/VirtualBox/Windows_7.xml' (VERR_FILE_NOT_FOUND)
  [!] Component   = Machine, Interface: IMachine, {ea6fb7ea-1993-4642-b113-f29eb39e0df0}
  [!] Callee      = IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}</pre>