Today I got the following error after setting a web site in IIS to use HTTPS/SSL and trying to start the site:

“The process cannot access the file because it is being used by another process. (Exception from HRESULT: 0x80070020)”

Not a very helpful error message. Fortunately, I remember seeing something like this before when another application was already using port 80 or 443 (the standard HTTP and HTTPS ports) and IIS couldn’t attach to them. In this case it was that ubiquitous communications tools for developers and non-developers alike: Skype.

Skype has an advanced setting that allows it to use ports 80 and 443 to accept incoming connections, but this doesn’t work well when IIS wants to use those ports too.

I imagine that this combination of installed software (IIS and Skype) is a very common pairing for all of us Microsoft web developers, so I thought I would share the solution. It’s simple, really. Just turn off Skype’s ability to use ports 80 and 443, then restart Skype.

The option is under Tools > Settings, Advanced Connection, then uncheck “Use port 80 and 443 for additional incoming connections”.