Backup to my new WD My Passport

Did you format the new WD My Passport, also please make sure you do not use any of the WD software they may have included. Simply format the drive to Mac OS Extended (Journaled) using Disk Utility.

Also, when posting a question, please be complete. We have no context here so we need you tell us what you did.

Then format it please.

1. Open Disk Utility.
2. Select the external drive you want to format on the left hand side of the window.
3. Click the Erase button.
4. Select Mac OS Extended Journaled format from the drop down menu.
5. Click Erase and follow the prompts.

Glad you got it sorted out!