A problem of cache? I don't get any 404 pages.
Once you made the modification, the standard version should be OK (at least for what is badly done with rewrite rules).
If you install the latest version available on the WordPress directory, you will get this message:
All-in-One Event Calendar Notice: You are using the Lite Calendar. This edition of the plugin is no longer supported. Upgrade to the Standard Calendar for free
I won't advise you to use a "no longer supported" plugin.
