WD Elements won't let me drag/transfer files, why?

I just got a WD Elements and followed the instructions on reformatting (Knowledge Base #3865) I have MacOS High Sierra
It shows up on Desktop and in Finder. It just won’t allow me to transfer files.

What am I doing wrong?

I want to use it as external storage, not TimeMachine (I have another disk for that)

Restarting the computer worked. Sorry to bother you guys!