Cannot get old vdi on new Vbox of new SSD-drive

[Sheldon Cooper Fan]

Hello,
I could not find an entry about this issue: I installed a second harddrive on my macmini (SSD 128GB) and installed Lion on it. Migrating my software, everything went well except Virtualbox. It could not access the old vdi (I started it a year ago so creating version is rather old) either on the old disk nor in the new one. I installed VB 414 and followed several guides from the internet, but nothing works.
I get the error message:
The harddisk could not be opened /Users/myname/VirtualBox VMs/Win7/Snapshots/{44ea274f-5703-4806-bf8f-cbe97815cb64}.vdi

Parent medium with UUID {3410016c-f63f-4854-9ed9-16745d2b37ff} of the medium '/Users/Senge/VirtualBox VMs/Win7/Snapshots/{44ea274f-5703-4806-bf8f-cbe97815cb64}.vdi' is not found in the media registry ('/Users/myname/Library/VirtualBox/VirtualBox.xml').

Fehlercode:NS_ERROR_FAILURE (0x80004005)
Komponente:Medium
Interface:IMedium {53f9cc0c-e0fd-40a5-a404-a7a5272082cd}
Callee:IVirtualBox {c28be65f-1a8f-43b4-81f1-eb60cb516e66}

I could not find the mentioned VirtualBox.xml at all
I still have access to the old VB by starting MAC Lion on my old HD, or copy the old VB to the new one again via migration.
Any clues?
Thank you
Philip