As seen in the last blog entry
hen you click preview or export, the HTML5 exporter converts your project in to HTML, javascript and PNG images. It generates all the necessary code for your game to play on a web page. It also launches a local HTTP server to work around browser security restrictions.
Do you use a local server (like wamp or xamp) or something to help you make websites localy ?
From what I know there is a local server by default in Windows 7, and I think Ashley relies on it for the previews.
At worse, try to uninstall C2, redownload it and reinstall it. Maybe your first download got screwed at some point (it happens).