2 New Drives - Can't See - How to setup My Dual Book

So, I have a Dual MyBook drive that doesn’t have HDs in it. I have two 2000GB Seagate Barracuda drives. When I put both drives in, they will not mount. When I leave one in, on one side it mounts and I can erase/initialize it. When I take that out and put the other one in, on the other side, I can erase/initialize it also. But when I put both in, my Disc Utility won’t see them, and my WD app sees a drive but I can not do anything with/to them.

Do I have to set them up a certain way for them to be seen?

Any help would be greatly appreciated!

I could be because of the RAID controller integrated in the My Book Duo or Harware Encryption of the enclosure.

You should try contacting WD Support for this issue. They can answer better on such scenario.