我也碰到了这问题，后来自己搞好了，对话框里面应该还有更加具体的提示吧？我是因为一个光驱挂载有问题，你可以到~/.VirtualBox下修改一下Virtualbox.xml这个文件，你仔细看看这个文件里面的内容是否和你希望的相符合，要不你删掉这个文件也可以，再打开Virtualbox又会创建的，不过很多信息会丢失，建议你对照着改改，我就这样好了，祝好运，以下是我的Virtualbox.xml内容：
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!-- innotek VirtualBox Global Configuration -->
<VirtualBox xmlns="
http://www.innotek.de/VirtualBox-settings" version="1.2-linux">
<Global>
<ExtraData>
<ExtraDataItem name="GUI/LastWindowPostion" value="284,98,700,500"/>
<ExtraDataItem name="GUI/SuppressMessages" value="remindAboutAutoCapture,remindAboutInputCapture,remindAboutMouseIntegrationOn,remindAboutGoingFullscreen,remindAboutMouseIntegrationOff,remindAboutInaccessibleMedia"/>
<ExtraDataItem name="GUI/Input/HostKey" value="65508"/>
<ExtraDataItem name="GUI/Input/AutoCapture" value="true"/>
<ExtraDataItem name="GUI/LanguageID" value="C"/>
</ExtraData>
<MachineRegistry>
<MachineEntry src="Machines/XP/XP.xml" uuid="{df139cf0-a2e8-4a61-4aa2-07def011f191}"/>
</MachineRegistry>
<DiskRegistry>
<HardDisks>
<HardDisk type="normal" uuid="{daa929b4-5c3d-48af-079b-8b86b34ac81e}">
<VirtualDiskImage filePath="VDI/MYXP.vdi"/>
</HardDisk>
</HardDisks>
<DVDImages>
<Image src="/home/xiao/Desktop/xiao/XRMPVOL_CN.iso" uuid="{1c61a001-4443-42fb-43a7-e27a716a3830}"/>
<Image src="/home/xiao/.VirtualBox/VBoxGuestAdditions_1.5.0_OSE.iso" uuid="{7fdbea42-bf1a-411b-0b88-077708e1f1d2}"/>
</DVDImages>
<FloppyImages/>
</DiskRegistry>
<USBDeviceFilters/>
<SystemProperties HWVirtExEnabled="false" defaultMachineFolder="Machines" defaultVDIFolder="VDI" remoteDisplayAuthLibrary="VRDPAuth"/>
</Global>
</VirtualBox>