Similar problem but I've formatted
I have a similar problems, but I have already formatted Passport on my Mac I have been able to backup before, but now I can paste nothing to the Passport.
MacBook, iOS 10.1.1
Perhaps when you first asked a question, it had been
associated with an existing discussion; so when it was
relocated to create a new thread, the issue was lost.
You may need to choose another formatting option for
use with the external hard drive. Depending on which
type of formatting you choose, results may differ a bit.
With Disk Utility you can choose HFS+ Journaled among
others. If you aren't to place bootable systems on there
the format need not be a newer Apple format version.
..Which macOS or OS X version are you using this device with..?