为什么VirtualBox找不到名为Windows_7的注册机器？

每当我输入命令：

sudo VBoxManage setextradata Windows_7 "VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestEmule_TCP/Protocol" TCP

我收到以下错误：

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}

虚拟机已使用GUI创建。任何想法？

$ 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}