Apache httpd: make_sock: could not bind to address 0.0.0.0:80

When (re)installing httpd today, I ran into the following error message:

(OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. 
: make_sock: could not bind to address 0.0.0.0:80

As the error indicates, port 80 is unavailable presumably because some other program is using it. While I initially thought that my previous version of httpd hadn't uninstalled properly, it turned out that the culprit was Skype. Exiting Skype and restarting httpd fixed the problem. I also restarted the PC to confirm that the problem did not occur after bootup either.

I'm not sure. But the problem could well have gone away simply by restarting the system :)