DDPST - Security Tools Activation Does Not Recognize WD Passport as External Backup Drive

I'm going through the DDPST setup under Administrator Settings. I get to the point where it asks me to choose a backup location. 

I've tried a brand new 3TB WD Passport USB drive and a 500GB WD Passport drive that's at least 5 years old. in both cases I can browse to the drive and create a folder on it. 

When I select that folder as the backup location, I get the message "Backup locations's drive type must be either a removable or network drive".

It's obviously an external drive but doesn't seem to think so. 

This is a 7710 Laptop on W10.

Thanks.

Tom