NETSTAT -ab will give you a list of all open ports on your systen as well as the process name. Look for anything that has :443 in the port section of the IP and it should help you find the culprit.

On a desktop machine I'd suspect Skype, which can take over port 80 and 443 if you let it. If it's a server that's not likely though, but there may be some other HTTP server running on the server that *is* using that port already. Ports cannot be shared easily by multiple applications.

You can set up multiple sites on IIS using the same port if you use host headers (ie. custom domain names for each site), but IIS only supports 1 SSL connection per port per IP address.

+++ Rick ---

>Hi,
>
>I am trying to install a web application on the customer web server. The customer asked that I set up port 443 for this Site. But when I do and try to start the site I get the message that "Another Web Site maybe using this port". I can set up any other port # but the 443. How do I find out what site is using this port 443 (I checked all sites in the IIS and none is using this port, as far as I can see).
>
>TIA