Forwarding external port 80?

So on my home network, I ran into an issue today….

I have a website which I want to expose to the outside/externally through the default port (e.g. 80).  I go into my router and I enable port forwarding for the web server hosting the site:

Then I open up a browser (from an external network to ensure the test), and the browser hangs and then comes back with the following error after some time:

Network Error (tcp_error)
A communication error occurred: “”
The Web Server may be down, too busy, or experiencing other problems preventing it from responding to requests. You may wish to try again at a later time.

After scratching my head and trying different options (disabling the firewall, restarting router, etc.), this error persisted.  I am able to port forward other ports just fine such as RDP, FTP, but port 80 is not working for some odd reason.  I then combed through some forums and discovered that some ISPs apparently block the forwarding of port 80!  Why?  I have no idea, feel free to comment.

Anyway, so I resolved this by simply assigning a different external port which still resolves to the internal port 80:

This did the trick.  Frustrating, but it works…