Skype nearly got me into screaming this night. I was debugging an ASP.NET 2.0 problem and at some time the IIS started to behave very strange. The debugging in Visual Studio failed with error “Unable to start debugging on the web server. The server committed a protocol violation. Section=ResponseStatusLine” and any attempt to load a page from the local IIS server returned an empty page even for those that did not exist :). At some time (couple of hours lost) I saw in the IIS Management Console that the web site was not running at all. When I tried to start it I got the error “Unexpected Error 0x8ffe2740 Occurred” and the long awaited event log entry (there was no entry at the time I tried to start the web site) – Event ID: 115 Description: “The service could not bind instance 1.”. A quick google showed that this error is due to already opened port 80 and the web server just could not open and use that port. Indeed netstat –a showed that port 80 is already opened but there was no way to see who was using it. This is where TCPView, marvelous tool from Sysinternals, helped a lot (Update: I just found that netstat –b would display the owning processes of each connection.). There was Skype listening on port 80, obviously taken ownership of the socket during the number of restarts when I was debugging. How stupid is that?
Attention to all web developers who are using Skype! Make sure to uncheck the option for using port 80 and 443 from ToolsOptionsConnection dialog.