I've found that I need to do this a lot, especially when installing WAMP on a machine that I'm also running IIS on. I usually place Apache onto Port 81. To make this change in WAMP 2.1, use the following procedure: Open the http.conf file found in your /wamp/bin/apache/Apache2.2.17/conf/ folder. Search for the line that [...]
If you receive this error after installing WAMP, most likely you have another installation of PHP on your machine. This may have been installed using the Microsoft Web Platform Installer or by other means. The first thing you should do is un-install PHP. If this doesn't work, check to make sure that IIS and Apache [...]