I had that problem before. The problem is that your PC is viewing the two drives as the same device. There is a way to get past that but I don't exactly remember how I did it. I'll try to figure it out and post back.
Not sure what version of Windows you are using but go into Disk management and start by making sure you see both WD hard drives are listed. (They should be) Then change drive letter and paths and make sure each hard drive is different. You will then get a message saying the device has the same attributes to another drive on the system and it will ask you if you want it to be recognized as a separate device. Choose yes.
In disk management you have to right click the partition and then you will see the option to assign a drive letter and set paths.