Can't add a new folder in wd sync

I suddenly can’t add a new folder in wd sync on my laptop with windows 10. When i want to create a new folder i always get the following warning: cant connect with external server. Does anyone know a solution?

Are you creating the folder and then placing it in the sync folder on your laptop?

The following comes from the user manual.

Copying Into the My Cloud Folder

When you copy a file or folder into the My Cloud folder on your computer, the WD Sync software automatically copies it to the WD Sync folder on:

Your My Cloud device 
Any other computer in your network with the WD Sync software installed.