To clone a Virtual Box image do the following:
1. Copy the VM disk using following command    VBoxManage clonevdi SourceDisk.VDI TargetDisk.VDI2. Go To File -> Virtual Media Manager -> Add -> add the newly created disk (TargetDisk.vdi)3. Create a New VM from Machine -> New,   Type the new VM name,   Allocate Memory,   Virtual Hard Disk, Use Existing Hard Disk   Select the  Hard Disk you added in step 2.   Finish 
   Copying the Virtual Machine HDD to other location will not work. You have to explicitly use the VBoxManage command in order to create a clone image.