Each plugin (track) offers different configuration options. To find out what options are available you will need to read the documentation for the plugin in question. A list of these plugins is available from the plugin registry.
The config file is a Javascript object and, as such, must be properly formed. Object properties must be separated by commas, as must elements in an array. A common mistake is to add a comma after the last item in an object or array, or to miss a comma between two entries. More information about formatting can be obtained from JSON.org.
This is a consequence of the same origin policy, a security mechanism in modern browsers that prevents cross-site XHR. To get around this, you will need to configure your server as a reverse proxy. For more information, see connecting to a service.
I strongly recommend using Firefox with the Firebug extension enabled. This will quickly identify the exact source of errors in most cases. If you can't quickly resolve the problem, please contact me and I will try to help. Don't be shy to report problems.