Hi,
When I tried to open the file, the server says that there is an issue with your .htaccess file, so it denies access to the file automatically.
You can try reinstalling the plugin, to make sure the file was not deleted by accident, but this is more likely a server side problem.
I strongly suggest checking the .htaccess file in the root and sub folder (if they exist), as well as the file access permissions. Direct access to javascript, image and CSS assets should be permitted on the server.