The process cannot access the file because it is being used by another process.

Hi. I'm using BE 9.1 4691 together with a NAS - Buffalo LinkStation. I run two backups per night. First to the NAS and then a Duplicate job that takes this backup and shoves it to tape.  The above error is becoming more common so hence this question: What can possibly be using the first backup file on the NAS other than BE itself?  Can I add a delay factor between the two jobs? It looks like the first job does not release its hold before the Duplicate starts up.  I also happen to know that using Windows logons to the NAS (linux OS, I think) causes all sorts of problems if you log on twice from the same machine.  Pointers most welcome.  Thanks in advance.