Problem using on a PC transfer to Mac

WD External Drives External Drives for PC
1

I just bought the my book essential.  I have a ton of jpg files on my pc and my mac.  So i plugged it into my pc and dragged the photos in and saved properly.  I then connected to my Mac Book Pro and it will not allow me to move any files into it, also jpg files. It says it is unlocked and then I go to unlock and says it is.

Anyone help please?

Thanks