That is the most useless error message I think I have ever seen…sorry you have to deal with that.
My best guess would be there is an authentication error between your notebook, and the requested resource. So, either, in order to download whatever you are trying, you need to provide credentials, or only certain IP addresses are allowed access to that resource.
Perhaps, if you can open up the browser devtools, and look for more specific errors in the console or network tab? Otherwise, hopefully others will know more about this.