The most likely cause of this is that you have a DNS record entry in your DNS settings pointing to one of Cloudflare's IP addresses or a mistake in the CNAME's destination. Please login and change the record(s) to point to the IP address of your server. You could also be receiving this message if you are trying to CNAME a domain not on Cloudflare to a domain that is on Cloudflare. Since this creates a DNS lookup problem, since the domain is not on us, you would want to add the domain not on Cloudflare to us as well to resolve the issue.
If the IP shown in the "Your IP address" field is not the IP of your browser or browser-configured HTTP proxy, then your web server is most likely re-proxying our requests, which will not work properly and is due to improper DNS resolution by the web server. In other words, your web server is proxying requests to "www.example.com," but because Cloudflare has been activated for that DNS record, the web server is proxying those requests to a DNS record that resolves to Cloudflare IPs, resulting in cyclical requests and the "DNS points to prohibited IP" error screen with the IP of your web server's proxy IP. Web servers should be configured to resolve www.example.com to the internal NAT-ed IP, if applicable, or the public IP of the origin web server to prevent the problem.