We can't find the library that this folder is syncing with, probably because it was deleted or moved on the server. To continue ...

We can't find the library that this folder is syncing with, probably because it was deleted or moved on the server.  To continue syncing this folder, restore the library on the server, open the OneDrive for Business menu in your system tray and click 'Sync now'.  Otherwise, we recommend that you stop syncing this folder.