Data Protector 6.21 VE backup hangs

Hello.

When I try to backup my hyper-v machines, either on tape or on disk, the backup shows that it has completed successfully but it never finishes. It shows the drive as Inactive/Finished but the session is still In Progress.

Cell Manager is a Windows Server 2003 R2 Std.  with DP6.21 and latest patches.

Host is a Windows Server 2008 R2 Ent. with 2 virtual machines (both Windows Server 2008 R2 Ent.)

Cell Manager is also the Backup Host (the one with the Virtual Environment integration installed).

Disk Agent and MS Volume Shadow Copy integration are installed on host and virtual machines.

Host and virtual machines are imported in the cell as Data Protector clients. Furthermore, host is also imported as Hyper-V client.

Any ideas?

Thanks