This looks like NetBackup was setup to use a service account to operate (are you running version 10+?).
Try using the nbserviceusercmd command (bin\goodies folder) to change the service user (either to an existing user or to use the local service account or local system account).
Looks like a possibly simpler solution (I was assuimng you were running version 9.1+).
Have a look at this article and see if this resolves your issue:
Given the number of files/folders covered, it may take some time to remove the rougue SID.