Add more desktops in a group fails in vWorkspace 8 and Hyper-V 2012

Hello,

I have a Desktop group created and with 4 computers provisioned. Now I want to add more computers, but the provision fails with the following error:

Create failed.  CreateVM  CreateVfd failed! path  , error  CreateVfd  exception caught - message  Path cannot be null.Parameter name  path type  System.ArgumentNullException stack    at System.IO.FileStream.Init String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath    at System.IO.FileStream..ctor String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options    at FatVfdSysprep.SysprepVfd.CreateVfd String strVfdPath, VfdData vfdData, String

Any idea? Thanks