Getting this error on IIS? It's gotta be the most unhelpful error message ever, made worse by this advice from the boys at Redmond! Go ahead and rate that article a big fat ZERO.
You've got Skype installed, haven't you?
I've gotta be one of the most forgetful people on earth. Almost every time I do a format/clean install I forget this one. So I thought I'd put it in a blog article so that anyone else equally forgetful will find it when they Google the error! ;) [Other brands are available]
Basically, this error is because Skype uses port 80 to listen to calls as an alternative to its other port (25601) in case that gets blocked by a wall of fire.
To sort this, load up Skype and go Tools -> Options... then click Connection:
Uncheck the box that reads "Use port 80..."
Enjoy!