Can you reproduce this error in the browser? If so, it’ll be easier to debug.
The message you see if a bit of a catch-all error. It is directing you to check your site permissions for arc:
You need to set Automatic downloads to Ask or Allow.
However, it sounds like it might not be that simple in your case. An error should also be logged to the browser console.
Press F12 and choose the Console tab in Chromium-based browsers to view any errors. Please let us know what you see, for any other users experiencing this problem.
In any case, it’s probably better to continue troubleshooting in a new ticket on the support site.