BryanLee,
The WD Thunderbolt Duo and Velicoratpor MyBook will operation with only one drive. Any software RAID would be either degraded (RAID 1 - Mirror) or not functional (RAID 0 - Striped). Just delete the RAID in Drive Utility and everything should be good as just one or two drives (JBOD - Just a Bunch Of Drives). It will allow you to test the unit. I would try the drive in both slots to make sure that both work.
Enjoy!
