Usually that means that you don't have permission to save there, but could also mean that the drive is formatting in a way that can be read but not written (such as: MacOS can read NTFS, but not write to it).
Before we waste both your time and mine exchanging potentially irrelevant information, would you be so kind to specify whether you are on a Macintosh or a Windows PC?
If you're on a Mac, I may have a suggestion or two; if on Windows, I can't help you at all.
Thanks in advance.
I have a new mac & have downloaded & paid for CC