I am having the same problem and have visited the forums "olivers" directs us to. From what I can see when you adjust the variables in the cforms.js file (in the js folder of the plugin), make sure you have removed the "//" on the line you are editing... like this:
// e.g. try instead:
// var sajax_uri = '';
var sajax_uri = '/FORUMS/wordpress_music/'; // --> URIprefix = your Blog's prefix!
// var sajax_uri = document.location.pathname;
So if your WP install is directly in the root of your site in a folder called wordpress, that line you see without the "//" would be:
var sajax_uri = '/wordpress'; // --> URIprefix = your Blog's prefix!
Hope that helps.