Shared files - "This directory is unavailable, please check the logs or contact the administrator"

Hello, i am a new user of nextcloud and i am having problems accessing shared files from another user. I’m using the web browser GUI in mozilla firefox, on a windows 7, 64 bit.
First i receive an e-mail inviting me to accept the shared files, and when i click the link button, i’m directed to following web page (see uploaded image) with the following message: “This directory is unavailable, please check the logs or contact the administrator”

Because i’m a new user, i don’t know where to begin looking for the problem.
I welcome any help possible.

Many thanks in advance,
Ossa