In case you don't have this message doc, looks like a
message they don't expect to ever see...

ANS4001E Error processing ' filespace-name': file
space not known to server.
Explanation:  The number defining the
correspondence between drive letter or file
(domain name) and volume label is not
known to the server.
System Action:  Processing stopped.
User Response:  Report the program
error to your service representative.

Maybe you're attempting to store backup data under a
volume-label which is different than existing data
for the same client and UNC file space name combination.
There's a history of conflicting ways to handle this on
NT, so maybe check "Q FI" for your client, to confirm.
Also, try using GUI versus command line... sometimes
the code path is different, things work one way but not
the other (and some loop holes exist in one but not the
other.)

Hope this helps,

Don France
PACE