Ciao 

i problema da te indicato a me direttamente non è mai capitato.

Ma visto i post che ci sono proverei a fare questi comandi:

1. Click Start, click Run, type Regedit, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\EventSystem\{26c409cc-ae86-11d1-b616-00805fc79216}\Subscriptions
3. On the Edit menu, click Delete, and then click Yes to confirm that you want to delete the subkey.
4. Exit Registry Editor.
5. Click Start, click Run, type services.msc, and then click OK.
6. Right-click the following services one at a time. For each service,  click Restart: 
   • COM+ Event System
   • COM+ System Application
   • Microsoft Software Shadow Copy Provider
   • Volume Shadow Copy
7. Click Start, click Run, type cmd, and then click OK.
8. At the command prompt, type vssadmin list writers, and then press ENTER.
9. If the VSS writers are now listed, close the Command Prompt window

E poi proverei nuovamente a convertire la VM.

Prima di eliminare la chiave dal registro farei un backup del registro.