装了一个win7x64，准备打开ubuntu12.04，后来竟然报错（最新版的virtualbox，VirtualBox-4.3.18-96516-Win）：
也没找到什么原因，网上查了之后，禁用了win7自带主题，发现也没有奏效。
贴一下log，也没看出所以然：
VirtualBox COM Server 4.3.18 r96516 win.amd64 (Oct 11 2014 13:21:57) release log
00:00:00.000000 main Log opened 2014-11-08T08:42:16.804322600Z
00:00:00.000000 main Build Type: release
00:00:00.000000 main OS Product: Windows 7
00:00:00.000000 main OS Release: 6.1.7600
00:00:00.000000 main OS Service Pack:
00:00:00.140400 main DMI Product Name: 28747GC
00:00:00.171600 main DMI Product Version: ThinkPad SL410
00:00:00.171600 main Host RAM: 2936MB total, 1870MB available
00:00:00.171600 main Executable: C:Program FilesOracleVirtualBoxVBoxSVC.exe
00:00:00.171600 main Process ID: 3932
00:00:00.171600 main Package type: WINDOWS_64BITS_GENERIC
00:00:00.171600 Loading settings file "C:UsersAdministrator/.VirtualBoxVirtualBox.xml" with version "1.12-windows"
00:00:00.795601 usbLibDevCfgDrGet: DeviceIoControl 1 fail winEr (31)
00:00:01.123202 HostDnsMonitorProxy: Host's DNS information updated:
00:00:01.123202 DNS server 1: 192.168.2.1
00:00:01.123202 DNS server 2: 0.0.0.0
00:00:01.123202 VDInit finished
00:00:01.138802 Loading settings file "C:UsersAdministratorVirtualBox VMsmmmmmm.vbox" with version "1.13-windows"
00:00:06.273271 ERROR [COM]: aRC=VBOX_E_INVALID_VM_STATE (0x80bb0002) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={Machine} aText={Machine is not locked for session (session state: Unlocked)}, preserve=false
00:00:12.105753 ERROR [COM]: aRC=VBOX_E_OBJECT_NOT_FOUND (0x80bb0001) aIID={3295e6ce-b051-47b2-9514-2c588bfe7554} aComponent={ExtPackManager} aText={No extension pack by the name 'Oracle VM VirtualBox Extension Pack' was found}, preserve=false
00:00:12.167261 ERROR [COM]: aRC=VBOX_E_IPRT_ERROR (0x80bb0005) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={SessionMachine} aText={Saved screenshot data is not available (VERR_NOT_SUPPORTED)}, preserve=false
00:02:46.806671 ERROR [COM]: aRC=VBOX_E_INVALID_VM_STATE (0x80bb0002) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={Machine} aText={Machine is not locked for session (session state: Unlocked)}, preserve=false
00:02:51.247051 ERROR [COM]: aRC=VBOX_E_OBJECT_NOT_FOUND (0x80bb0001) aIID={3295e6ce-b051-47b2-9514-2c588bfe7554} aComponent={ExtPackManager} aText={No extension pack by the name 'Oracle VM VirtualBox Extension Pack' was found}, preserve=false
00:02:51.297557 ERROR [COM]: aRC=VBOX_E_IPRT_ERROR (0x80bb0005) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={SessionMachine} aText={Saved screenshot data is not available (VERR_NOT_SUPPORTED)}, preserve=false
00:03:06.024594 ERROR [COM]: aRC=VBOX_E_INVALID_VM_STATE (0x80bb0002) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={Machine} aText={Machine is not locked for session (session state: Unlocked)}, preserve=false
00:03:10.461978 ERROR [COM]: aRC=VBOX_E_OBJECT_NOT_FOUND (0x80bb0001) aIID={3295e6ce-b051-47b2-9514-2c588bfe7554} aComponent={ExtPackManager} aText={No extension pack by the name 'Oracle VM VirtualBox Extension Pack' was found}, preserve=false
00:03:10.504483 ERROR [COM]: aRC=VBOX_E_IPRT_ERROR (0x80bb0005) aIID={480cf695-2d8d-4256-9c7c-cce4184fa048} aComponent={SessionMachine} aText={Saved screenshot data is not available (VERR_NOT_SUPPORTED)}, preserve=false
后来安装了旧版本：VirtualBox-4.2.16-86992-Win
虽然能打开了，安装tools的时候竟然不识别xwindow。
好吧，于是下载其他版本试试看，下载了一个4.3.10 版本的virtualbox，终于可以用了。
这件事情给我的经验教训是对于有些软件，不要尝试最新版本。百度贴吧上对于virtualbox有各种乱七八糟的问题的讨论。
这个东西毕竟是免费的，也不能怪他。之前用的vmware也用的很不顺心，后来只能用virtualbox。感觉vmware的bug比virtualbox多多了。