If you have installed a Domino Server with Http Server enabled for both Mail and Application, you might face a problem on Win2000 Advanced Server or NT Server.
If, after you started your Domino Server for the first time, the HTTP Server task shuts down it will have an Error saying: "Unable to bind to port : 80, port is not available or may be in use."
Here is the fix:
go into your Server Document glt; go to: Ports Tab glt; Internet Ports: Make sure that the WEB(HTTP/HTTPS) is enabled in TCP/IP Port Status and the Port Number is 80. then go to: Server Tasks Tab glt; Internet Cluster Manager: check the ICM HTTP Port settings. make sure the TCP/IP Number is different form the number above. save and close the server document. Now go to your Control Panel: Open the "SERVICES" Panel. search for: Windows Internet Name service Stop this service.Then check out if you OP has a Microsoft Internet Server. If yes, go to the Internet Service Manager (not the HTTP). Check out if any other services running, if so, stop them.
After that, go back to your Domino Server Console: use the command: load http, which will start the http server task. If the server starts and does not stop, everything is fine, otherwise, check for more Internet settings in your OP.