Unable to download Host & Target components in SDK Manager

I have a fresh install of SDK Manger, however when I attempt to download any of the components the download fails.
I have checked the logs in the SDK Manager Terminal window and see two types of error:

18:22:23 ERROR: OpenCV on Target: The .mtd file is corrupt. Start a new download.
18:22:24 ERROR: OpenCV on Target: DevZone get download url failed: HTTPError: Response code 401 (Unauthorized).

Does anyone have the same issue, or a fix?

Many thanks

I found a similar, newer, thread here: