Resize error: How to decrease a VM?

[Erich_13]

Hello everybody,
unfortunately i resized the hard disk of a VM to 14TB instead of 14GB with the VBoxManage.exe. At the same time i updated VirtualBox from version 3.2 to 4.2. Now the VM doesn't start anymore, the guest system (XP) generates a blue screen.
I don't know if it's the update of VirtualBox or the resize operation that prevents the start of the VM.

It is not possible to resize (decrease) the VM to a suitable value again (Progress state: VBOX_E_NOT_SUPPORTED).

Is there a way to reset the virtual machine to a healthy state or at least to recover data from this machine?

[Perryg]

Recover from the backup you made before you started this dangerous task. If it were not so large I would say to simply attach it to an existing guest as a second drive and extract your data, but since it is 14 TB I don't know if that will work or not.

[mpack]

XP will bluescreen because it doesn't support drives larger then 2TB using native drivers.

The only known solutions for this problem are: (a) restore from a backup, or (b) hack the VDI file header with a hex editor as discussed here.

[Erich_13]

Thank you for the replies, Perryg and mpack!
I attached the VM to an existing Guest (Win7, 64bit). This triggered a checkdisk operation that lasted 19 hours. Sadly, the drive couldn't be accessed afterwards.
But surprisingly the big VM now starts with Virtual Box! There is a connection to the host, i can delete, create and edit files, but copy and paste doesn't work anymore. Internet Explorer won't start, Firefox does but without connection to the internet.
Maybe i should try to hack the VDI file header as suggested...

[mpack]

I hope you at least made a backup before making those additional changes...

[Erich_13]

I succeeded in saving the data from the corrupted VM after a repair installation of Windows XP!
Next thing is to create a new XP machine. I refrain from hacking the VDI file.

Anyway, thank you both very much for your help!
I at least learned not to undervalue a backup...