Unable to start web site IIS HRESULT: 0x80070020)

I'm trying to publish a web site with a self-created SSL certificate on my own IP. After I added the web site to the IIS and tried to run it, I get this error and I'm unable to start the web site.

Internet Information Services (IIS) Manager - The process cannot access the file because it is being used by another process. (Exception from HRESULT: 0x80070020)

What can be the reason of that problem?

Check this http://support.microsoft.com/kb/890015/en-us

Another process is using port 80 or port 443 on the computer that is running IIS. By default, IIS uses port 80 as the default TCP port and port 443 for Secure Sockets Layer (SSL).

To further elaborate Nacho's (correct) answer, from here:

Run the following command from a command prompt to find the PID of the process which is using TCP port 80 and/or 443 (hint: for 443, it's probably Skype):

netstat -aon | find ":80" 
netstat -aon | find ":443"

You will see an output similar to the following. Remember the actual PID will vary from case to case.

TCP    0.0.0.0:80            0.0.0.0:0              LISTENING       3604 
TCP    0.0.0.0:443           0.0.0.0:0              LISTENING       3320

Now using Task Manager you can easily find out to which process the above PID belongs and take appropriate action.