[Veritas-bu] Windows disk-image backup

This is probably a stupid question, but I'm trying to take a disk-image
backup on a Windows NT server. These are the errors I get :

Date  Time  Media Server      Client      Severity    Job ID      Type
Description

19/12/02    15:31:35    obelix      obelix      Info  102   Backup
added backup job (jobid=102) for client obelix, policy Windows-backup,
schedule Full-backup part 0 to NetBackup scheduler work queue
19/12/02    15:31:35    obelix      obelix      Info  102   Backup
started backup job for client obelix, policy Windows-backup, schedule
Full-backup on storage unit disk
19/12/02    15:31:35    obelix      obelix      Info  102   Backup
client obelix handling path /\\.\E:
19/12/02    15:31:36    obelix      obelix      Info  102   Backup
begin writing backup id obelix_1040308295, copy 1, fragment 1
19/12/02    15:31:38    obelix      obelix      Warning     102   Backup
from client obelix: WRN - can't lock raw device for read: \\.\E: (WIN32 5:
Access is denied. )
19/12/02    15:31:39    obelix      obelix      Info  102   Backup
successfully wrote backup id obelix_1040308295, copy 1, fragment 1, 1
Kbytes at 0.492 Kbytes/sec
19/12/02    15:31:39    obelix      obelix      Info  102   Backup Status
the requested operation was partially successful
19/12/02    15:31:39    obelix      obelix      Error 102   Backup
backup of client obelix exited with status 1 (the requested operation was
partially successful)

Do I miss something or is this because the drive is busy and therefore
can't be locked ? Since I don't have a tape library for the moment, I tried
to write to a disk storage unit on another partition.