Keep the following in mind when debugging your ezjscore setups:
To test that a network connection to the JavaScript libraries is not a problem, disable the ezjscore.ini[eZJSCore]LoadFromCDN setting.
Make sure you have set up the proper rewrite rules for CSS and JavaScript packing. These are noted in the INSTALL document that comes with ezjscore. You can also disable ezjscore.ini[eZJSCore]Packer to temporarily avoid the reliance on Apache rewrite rules.
For debugging calls to the server, up-to-date versions of Firefox and Firebug make up the best environment. If your server call is not properly defined in ezjscore.ini, you will get a "500 Internal server error". If it is defined but you do not have access to the function or it is not callable, you will get a 200 OK request, but with the error "Not a valid ezjscServerRouter argument: <input_arguments>". To make sure it is not a permissions issue, log in as an administrator user to the siteaccesses you are testing.
As noted earlier, the packed JavaScript and CSS files stored in the public cache folder are not cleared by the automated clearing tools (for example, ezcache.php). They must be manually removed from the file system. This will be fixed in future versions.