Unexpected error 0×8ffe2740 occurred in IIS 5.1

I've been getting 'Unexpected error 0x8ffe2740 occurred' under IIS 5.1 when trying
to start the website today and just went about fixing it. A quick google discovered that
it's due to another application using port 80. I remember having this problem once
before and the culprit was Skype. Closing down
Skype sorts out the problem.

This post explains
how to stop Skype from using port 80 if its free.