Volume Shadow Copy and NTBackup

Backups using NTBackup fail with the error message below. The backup works if
I manually start the Volume Shadow Copy service first. The problem is the
Volume Shadow Copy service stops shortly after the backup completes. Is this
normal? So scheduled backups fail because Volume Shadow Copy is not started.
How can I get the Volume Shadow Copy service to keep running or is it even
supposed to? I haven't even tried using VSS yet for shared folders. I just
want my backups to work on a schedule. Thanks!

Backup Status
Operation: Backup
Active backup destination: File
Media name: "6-20Shared.bkf created 6/20/2006 at 10:12 AM"

Volume shadow copy creation: Attempt 1.
Timeout before function completed

Error returned while creating the volume shadow copy:0xffffffff.

Error returned while creating the volume shadow copy:ffffffff
Aborting Backup.