Remote Access Works From Local PC But Not For Remote Computers

I use the WD MyCloud file-server system to securely access files I work on with other contributors. I am the administrator.
One remote user had no prior web access problems, but now cannot access his assigned folders. When I use his email address and password (locally), I can log into his account and can access folders and files.
The remote user has this same problem on both a PC and on a Mac, on both of which he had web access before. It appears that for the remote user the password is accepted but that there is a problem accessing the folders.
I rebooted the MyCloud; this made no difference.

Does anyone have an idea how to solve this?