I ran into a similar problem.
When upgrading some remote offices from a netware 3.x server to an nt 4 server, I tried to use the backup tapes to restore the user data. The backups were done using arcserve 6 for netware with an exabyte 8mm drive. We connected the same drive to the nt box and used arcserve 6.61 workgroup for nt. After merging the tapes, I was able to see the files, but I could not restore any. There was a message unable to create the netware root, or the job would just fail with no message or files restored. I tried restoring to other location with and without the agent. I tried all options for creating the directories. I tried arcserve advanced edition, no luck. I tried both workgroup and advanced with and without SP1 or SP2, no luck. I even tried while standing on my head, (it was late and I was away from home), no luck. I finally gave up and copied files through a workstation. That worked.
This may be a "feature" of arcserve meant to prevent anyone from actually using their product to save time and effort.