just a thought -
I know you are writing to disk, but double check that you have not set "eject-on-end" in the job. With a removeable drive, BackupExec may be waiting for a response to a "remove media" prompt
I haven't play with BEMCMD much lately, but with regular jobs you can specify actions to be taken when different Alerts come up. possible you can set it so that "OK" is automatically replied when the remove media Alert comes up