This can occur for several factors, to correct, follow the procedures below:
1. Access the control panel - cPanel in the "Hotlink Protection" option and if it is active, disable it. Just leave this option active if you have knowledge or if you really want to block the access of some link.
2. Leave the files that are inside the "public_html" with the permission 644 and the 755 directories.
3. Now go to the link that was displaying the error and update with Ctrl + F5.
If the error still occurs, please contact our technical support to help you!