What would cause Website Insights to present a 403 error on a site?

If the site doesn't exist? Or if the URL has been misspelled?

The site does exist and the url is ok... https://www.globalsteelbuildings.ca

Any other thoughts?

I tried accessing your site with Website Insight, and the first thing I noticed, was that it took quite some time, then I got the attached error. I tried both with http and https, the error was the same in both cases. I'm also attaching the saved project file for your site.
Further I tried opening the site in a browser after I added /index.html to the URL and also adding just /index.htm. Both of them produced a 404. I then tried adding /index.php, and that opened the 'home' page.

I don't know if I'm anywhere near a definition of your problem. If you don't get any better reply here in the user forum, then I'd suggest that you contact CC support directly.

I got a 403 error and it stopped almost immediately...not sure what's happening.

You need to discuss it with the CC support. Just open a ticket by clicking on your name up in the right corner of this page.

The site loads for me.

You mean in the browser? It loads for me too, but the problem appears when running it through Website Insight.

Perhaps the Inspector panel of Firefox Developer Edition (JPG files attached) may give a clue.

Frank

Good idea, Frank. I was just looking at the validation of the html and css, and there are quite a few errors that should be fixed.