Just to confirm, Guest Access is turned on for the Server?
Also, what version of Server are you using?
We're still on 9.2 . Guest account is enabled but I don't think it could be related to the issue as the error happens even if you copy/paste the url in a browser.
We're upgrading to v10.1 next weekend, hopefully that's going to fix the issue.
I am having the EXACT same issue. We are using our own sites to embed the views in, and users like in your situation are thinking the site is broken causing a flood of emails asking why they can't see a view. It would be nice to be able to check the permissions then show them a page that says they do not have the needed permissions, and to contact someone to request this access. We do have guest access enabled, but the point is to prevent them from seeing all the reports.
CH, suggest you reach out to support on this one so that they are aware that it is an issue for you.
I have created the support case: 02598323. I'm making executive dashboards for some really important people at the 2nd largest telecom in US. I'm looking really bad to those people right now.... These are not technical people. If the error doesn't say permission denied, first assumption is that it's broke and so am I.