Hmm... Did you check the Log4NET log files too, just in case? This video will help you find them. :)
Also, do you have any security in front of the website that might be helping to protect it, such as a firewall, CDN, and/or a WAF? They might be getting in the way. To determine this, you may want to use the Network tab in the Web Developer Tools to inspect the request and response for any additional error messages that might be occurring.
The following link will help you to how to inspect the requests and responses in your browser.