when I tried to open it back up again it gave this error.
I've tried everything I could find in the VBoxManage tool but without the header information the tool is useless.Failed to start the virtual machine win_xp.
Medium '/home/tanglin/.VirtualBox/HardDisks/win_xp.vdi' is not accessible.
Could not open the hard disk '/home/tanglin/.VirtualBox/HardDisks/win_xp.vdi'.
VDI: invalid header in '/home/tanglin/.VirtualBox/HardDisks/win_xp.vdi' (VERR_VD_VDI_INVALID_HEADER).
VD: error opening image file '/home/tanglin/.VirtualBox/HardDisks/win_xp.vdi' (VERR_VD_VDI_INVALID_HEADER).
In any case I found a description of the header format, but the chances of fixing it by editing the header manually are slim.
Is there any possible way to fix this? any help would be greatly appreciated.