The link you provided has an https type secure prefix and gives me a warning that the security certificate expired about 4 days ago (So Sept 12). It is not a secure site.
If you go to Altium here: https://www.altium.com/circuitstudio/circuitstudio-support#question-103
There is a link to the documentation. It uses http address rather than https.
Thank you Thomas, now it's working fine
and all of it's hierarchical links give an error of "Error! Not private" or something like this. This didn't happened last week. Can somebody from Altium or element14 fix it??
It's pretty hard to find support on the Altium webpage, btw.