Provides a back end secure area to upload and share files. Perfect for a simple intranet file sharing site. Supports large file uploads.
You may have a theme or plugin that re-registered jquery. Review your theme for any calls to: wp_deregister_script().
If found, make sure the add_action that calls this code uses: wp_enqueue_scripts/admin_enqueue_scripts
If you find a plugin that does this, contact the author and encourage them to properly override jquery.
Your web provider likely has mod_security enabled for your site. You should be able to contact them and have it disabled or updated to support applications which make use of AJAX posting.
Make sure you are running the lates version of Omni Secure Files.
You probably have WP_DEBUG enabled, which in some cases can output extra text into downloads.