WordPress returns unfound file only when cacheing enabled-Collection of common programming errors

Seems like a simple problem, but I can’t find an answer.

With cacheing disabled, everything works fine. With cacheing enabled the following javascript include returns a WordPress ‘page unfound’ error.

http://myserver/wp-content/plugins/myplugin/js/jquery.cycle.all.min.js

I’m disabling the cache using the Firefox web developer tool, but I can’t see that that should have any bearing in the issue. For some reason, WordPress can’t find a legit file.

The script is properly registered and queued with the following code:

 wp_register_script("jquery.cycle.all.min.js", $plugin_url . '/js/jquery.cycle.all.min.js', 'jquery');
 wp_enqueue_script("jquery.cycle.all.min.js");