BE 2010 won't use empty disk folder

Hello and thanks in advance for any help you might be.  

Problem:  BE 2010 keeps trying to backup to a full disk folder when I have another disk folder empty.  I just inheirited this setup and am new to BE.  I have tried to google this problem but have not been able to find an answer.

Under the Devices tab I have 4 disk based backup devices defined.  Simply Disk-Folder-1, ... Disk-Folder-4.  Folders 1-3 are full, folder 4 is empty.

I have a media set called  VMware-Incremental

I have a job that uses VMware-incremental.  The job keeps trying to backup to Disk-Folder-2 which is full, how do I tell it to use 4?

I'm at a loss to determine how to tell what media set uses what device.

Any Help will be greatly appreciated.