Ron,
Please see "note 4" on page 22 of the v5.0.1 admin guide. I bet this is what you are running into.
Note 4: If the Thinware vBackup server is a member of an Active Directory domain all non-interactive user sessions (such as user sessions created by scheduled tasks) must use a domain user account when using Thinware vBackup to execute backup jobs. Failure to set scheduled tasks to run under a domain user account may cause backup jobs to fail due to licensing errors.
Also, please tell us more about your setup. You should be able to get much better than "reasonable" backup speeds with the latest version of vBackup. Maybe we can provide some pointers.